Ray Fisman on Swedish school vouchers

Ray Fisman reports on the Swedish experience with vouchers and how it hasn't quire worked out as well as one might hope.  Ray Fisman isn't a naïve opponent of school reform -- he has been willing to discuss some rather strong findings arguing for improvements in how we handle teachers.  But he is pretty rough on Sweden, which apparently has more students going to for profit schools than anywhere else in the developed world. 

He rather clearly points out the basic problem:

None of this is terribly surprising—in econ 101 we learn that markets work their magic when buyers and sellers are well-informed about what’s getting bought and sold, and can therefore transact with one another without fear of getting conned. The apparent failure of the Swedish schooling experiment is a lesson in the inability of markets to solve problems where it’s hard to compare the educational “product” that’s offered, and the outcomes you can observe are subject to manipulation. It’s also a reminder that the cold, hard calculations of markets aren’t necessarily suited to the realm of education. Governments don’t shut schools because they fail to turn a profit. Private equity firms do. The parents of more than 10,000 students learned this difference the hard way last year, when the Danish private equity group Axcel abruptly announced its exit from the Swedish school market, stating that it could no longer cover the continued losses.

If we had really good, real time information on educational quality then this would be a less difficult problem.  After all, if informed decisions can be made then it makes sense that a liberal country like Sweden would want to empower parents to make the best decisions for their children.  Now, it is possible to argue that tweaking some feature of the Swedish approach could result in better outcomes -- much is possible.  But these sort of ecological examples certainly raise the bar for evidence of this approach working when it is fully scaled up (unlike something like KIPP which isn't necessarily intended to scale to all children in the US). 

Consistency

I was looking at Andrew Gelman's blog and saw his discussion of Ray Fisman's piece on compensation. I was especially struck by this statement:

Yet this aversion to pay cuts isn't good for workers or the American economy more broadly. More people end up losing their jobs than if wages were more flexible, and there are serious long-term consequences for the workers who lose their monthly paychecks. The negative impact on a worker's earnings, health, and even the earning prospects of his children lasts decades beyond the pink slip's arrival. Creative solutions—like the furloughs that cut government salaries in California and elsewhere—might help to make lower pay more palatable, by presenting the cut as a temporary measure and by creating at least the illusion of a lower workload. If we can find other ways of overcoming the simmering resentment that naturally accompanies wage cuts, workers themselves will be better for it in the long run.

I wonder how this links with tax increases. Greg Mankiw seemed to be quite displeased by the prospect of tax increases (which are a form of reducing compensation).

If this relation works the same way, then there are two implications:

1) Tax cuts are a terrible idea as a way of providing economic stimulus as they will do little to increase output (3 hours according to Fisman's experiment) but will be greatly resented if they are rescinded

2) High taxes (like low pay) seems to have little effect on income so if you rise taxes then you should raise them by a lot so you only feel the pain of resentment once.

I am not sure that this position is correct, but it sure is thought provoking.

Oh, Canada -- another interesting omission in "Clean Out Your Desk"

We're back with our ongoing coverage of Ray Fisman's recent article in Slate which ran with the provocative tagline "Is firing (a lot of) teachers the only way to improve public schools?" (notice that he didn't say "a way" or "the best way").

If you tuned in late, here's what you need to know:

Dr. Fisman starts by discussing a presidential commission report from the early Eighties that said the damage done by our poor educational system was comparable to an act of war. This somewhat apocalyptic language has since become a staple of the reform movement. It grabs the attention, justifies big, expensive, untried steps and sets up a false dichotomy between action and inaction.

The proceedings are then handed over to Joel Klein. Klein builds on the verge-of-disaster theme by invoking the United States' low ranking on the Organization for Economic Co-operation and Development's PISA tests. I've commented at some length on the implications of citing PISA while completely ignoring the better-established and well-respected TIMMS even when the discussion shifted to elementary schools where the TIMMS scores would seem to be far more relevant. (The term cherry-picking did come up.)

For now, though, let's grant Chancellor Klein and Dr. Fisman the benefit of the doubt. Let's say we accept the premise that OECD's PISA rankings are such a good and reliable measure of the state of a nation's schools that we don't even need to look at other metrics. We'll even stipulate for the sake of argument that a bad PISA ranking is sufficient grounds for radical measures. With all of these conditions in place, take close look at the next part of Dr. Fisman's article:

What could turn things around? At a recent event that I organized at the Columbia Business School, Klein opened with his harsh assessment of the situation, and researchers offered some stark options for getting American education back on track. We could find drastically better ways of training teachers or improve our hiring practices so we're bringing aboard better teachers in the first place. Barring these improvements, the only option left is firing low-performing teachers—who have traditionally had lifetime tenure—en masse.

The emphasis on better teachers—through training, selection, or dismissal—comes from the very consistent finding that improving faculty is one of the best, most reliable ways to improve schools. If the person standing at the front of the classroom has raised the test scores of students he's taught before, he's likely to do so again.

But how do you get good teachers in the classroom? Unfortunately, it turns out that most evidence points toward great instructors being born, not made. National board certification may help a bit, a master's degree in education not at all. It's also difficult to pick out the best teachers based on a résumé or even a sample lesson. It takes a year or so before evaluators (and even teachers themselves) know who is really good at getting kids to learn, and few qualifications are at all correlated with teaching ability. Candidates with degrees from prestigious colleges—the type where Teach for America does much of its recruiting—do a bit better, but not much.

Here's the gist of Dr. Fisman's premise:

1. According to PISA (the test that trumps all other tests) the state of U.S. education is dire;

2. We need to improve the quality of our teachers "through training, selection, or dismissal";

3. So far, no one has found a way to make training or selection work.

If we want education to do well we might just have to start firing teachers en masse, and by "do well," we mean outscore other countries, which raises the question, "How do other countries find all of those natural teachers?"

Of course, comparing educational systems of different countries can be tricky but we should at least be able to look at Canada. It's a fairly large industrialized country. Not that different economically. Very similar culturally with a comparable K through 12 educational system that has to deal with English as a second language (huge immigrant population), relies on roughly the same type of teacher training/certification that we use and continues to pull teachers in with promises of good job security.

In terms of this discussion, the biggest difference between the two countries could well be Canada's somewhat reactionary approach to reform (for example, only one province, Alberta, allows public charter schools). With such limited school choice and no real attempt to clean out the deadwood from behind the podium, the Canadian educational system looks a lot like the American system before the reform movement.

And how is Canada doing on the PISA math test?

From Measuring up : Canadian Results of the OECD PISA Study:

One way to summarize student performance and to compare the relative standing of countries is by examining their average test scores. However, simply ranking countries based on their average scores can be misleading because there is a margin of error associated with each score. As discussed in Chapter 1, when interpreting average performances, only those differences between countries that are statistically significant should be taken into account. Table 2.1 shows the countries that performed significantly better than or the same as Canada in reading and mathematics. The averages of the students in all of the remaining countries were significantly below those of Canada. Overall, Canadian students performed well. Among the countries that participated in PISA 2006, only Korea, Finland and Hong Kong-China performed better than Canada in reading and mathematics. Additionally Chinese Taipei performed better than Canada in mathematics.

That puts them in the top ten (in science they were in the top three). Now let's review the United States' performance (quoting Dr. Fisman):

Despite nearly doubling per capita spending on education over the past few decades, American 15-year olds fared dismally in standardized math tests given in 2000, placing 18th out of 27 member countries in the Organization for Economic Co-operation and Development. Six years later, the U.S. had slipped to 25th out of 30.

How do we reconcile these facts with Dr. Fisman's argument? As far as I can see, there are only four possibilities (if I've missing some please click the comment button and let me know):

1. Though PISA is a useful test, international PISA ranking may not be a sufficient measure of a country's school system;

2. Teacher quality is not a major driver of national educational performance;*

3. Teachers are made, not born. i.e. it is possible to train people to be good teachers;

4. Canada just got lucky and beat the odds hundreds of thousands of times.

If this were a PISA question, I hope no one would pick number four.



* This is really is a topic for another post, but I would expect the administrator effect to overwhelm the teacher effect. Perhaps Dr. Fisman is going to follow up with a Slate article on firing administrators who produce lackluster test performance.

Is Ray Fisman one of the best and the brightest?

Based on some of the feedback to my past few posts on Ray Fisman's recent Slate article, there's a point I should probably make explicit: given all available evidence including reliable first-hand accounts, Ray Fisman is an accomplished researcher and a good guy. Furthermore, I am working under the assumption that, like most people in the reform movement, Dr. Fisman is motivated by a deep concern about the state of education and a genuine desire to improve it. (I have also found this a safe assumption when dealing with the vast majority of the teachers Dr. Fisman would fire.)

I have singled out Dr. Fisman not because "Clean Out Your Desk" was exceptionally bad but because it was exceptionally representative. If this were an anomaly written by someone who was stupid or incompetent or had a grudge against teachers, it wouldn't be worth anyone's time to discuss, let alone exhaustively rebut it. This is something more disturbing.

David Warsh has drawn a relevant analogy between the reform movement and the run-up to Vietnam:

Remember the recipe for a policy disaster? Start with a handful of policy intellectuals confronting a stubborn problem, in love with a Big Idea. Fold in a bunch of ambitious Ivy League kids who don’t speak the local language. Churn up enthusiasm for the program in the gullible national press – and get ready for a decade of really bad news. Take a look at David Halberstam’s Vietnam classic The Best and the Brightest, if you need to refresh your memory. Or just think back on the run-up to the war in Iraq.

The education reform is filled with smart, well-intentioned people like Ray Fisman. Under the circumstances, that doesn't provide much comfort.

The Old Shell Game -- Why you have to keep your eye on Ray Fisman (and no, we're not quite through with the second paragraph)

Ray Fisman's Slate article "Clean Out Your Desk" is something of a greatest hits of the education reform movement, covering most of the standard arguments and carefully selected statistics that are brought up again and again by the advocates. It is, therefore, fitting that FIsman gets no further than the second paragraph before getting to this:

New York City Schools Chancellor Joel Klein often quotes the commission before discussing how U.S. schools have fared since it issued its report. Despite nearly doubling per capita spending on education over the past few decades, American 15-year olds fared dismally in standardized math tests given in 2000, placing 18th out of 27 member countries in the Organization for Economic Co-operation and Development. Six years later, the U.S. had slipped to 25th out of 30. If we've been fighting against mediocrity in education since 1983, it's been a losing battle.*

The OECD tests are the book of Revelations of the education reform movement, the great ominous portent to be invoked in the presence of critics and non-believers. Putting aside questions of the validity and utility of this test (perhaps for another post if my stamina holds out), we would certainly like to be in the top ten rather than the bottom.

But before we concede this one, lets pull out our well-thumbed copy of Huff and take one more look. Whenever one side in a complex debate keeps pulling out one particular statistic, you should always take a moment and check for cherry-picking.

Is Fisman distorting the data by being overly selective when picking statistics to bolster his case? Yes, and he's doing it in an egregious way.

Take a look at at the Trends in International Mathematics and Science Study. Here's a passage from the executive summary from the National Center for Education Statistics:

In 2007, the average mathematics scores of both U.S. fourth-graders (529) and eighth-graders (508) were higher than the TIMSS scale average (500 at both grades). The average U.S. fourth-grade mathematics score was higher than those of students in 23 of the 35 other countries, lower than those in 8 countries (all located in Asia or Europe), and not measurably different from those in the remaining 4 countries. At eighth grade, the average U.S. mathematics score was higher than those of students in 37 of the 47 other countries, lower than those in 5 countries (all of them located in Asia), and not measurably different from those in the other 5 countries.

We could spend some time in the statistical weeds and talk about the methodology of TIMSS vs. OECD's PISA. TIMSS is the better established and arguably better credentialed, but both are serious efforts mounted by major international organizations and it would be difficult to justify leaving either out of the discussion.

If Fisman had limited his focus to the education of high school students and simply ignored the data involving earlier grades, we would have ordinary misdemeanor-level cherry-picking. Not the most ethical of behavior, but the sort of thing most of us do from time to time.

But Fisman does something far more dishonest; he quietly shifts the subject to teachers in general and often to elementary teachers in particular (take a good look at the study that's at the center of Fisman's article).

This means that, when you strip away the obfuscation, you get the following argument.

1. The best metrics for tracking American education are international rankings on math tests;

2. The best way of improving America's education system is fire massive numbers of teachers, including those in areas where we are doing well on international rankings on math tests.

The bad news here is that we have a long way to go to make it through Fisman's article and it doesn't get much better, but the good news is that we're through with the second paragraph.




* Fought, for the most part with Klein and Fisman's battle plan but we've already covered that.

Starting from the beginning -- Ray Fisman's sins of omission

The centerpiece of Fisman's recent Slate article, "Clean Out Your Desk," is a deeply flawed analysis proposing that four out of five probationary teachers should be fired, but the problems with the article aren't limited to that one piece of research; they permeate the article, starting with the very first two paragraphs:

In 1983, a presidential commission issued the landmark report "A Nation at Risk: The Imperative for Educational Reform." The report warned that despite an increase in spending, the public education system was at risk of failure "If an unfriendly foreign power had attempted to impose on America the mediocre educational performance that exists today," the report declared, "we might well have viewed it as an act of war."

New York City Schools Chancellor Joel Klein often quotes the commission before discussing how U.S. schools have fared since it issued its report. Despite nearly doubling per capita spending on education over the past few decades, American 15-year olds fared dismally in standardized math tests given in 2000, placing 18th out of 27 member countries in the Organization for Economic Co-operation and Development. Six years later, the U.S. had slipped to 25th out of 30. If we've been fighting against mediocrity in education since 1983, it's been a losing battle.

Notice that strange gap of more than a quarter century? Other than mentioning increased spending per capita* and citing a couple of ominous sounding statistics, Fisman doesn't say a word about what happened since. There is no mention of what the response was to "A Nation at Risk." You could easily come away with the impression that there was no response, that educators had simply gone on with business as usual.

This is a common rhetorical trick in the educational reform movement.: to point out various facts suggesting a dangerous decline over the past two or three decades then quickly change the subject (sometimes citing "A Nation at Risk" to add a note of the Cassandra Syndrome). If only we had done something then, we wouldn't be on the precipice now.

The primary flaw in this narrative is that there was a response to the report, it was swift and sweeping, and mostly it consisted of the types of change reformers like Fisman, Klein, and Ben Wildavsky continue to push for to this day: importing techniques and philosophies from the private sector; encouraging privatization and entrepreneurs; basing the evaluation of schools on objective metrics (particularly standardized tests of student performance).

By the late Eighties, when I went into teaching, it was difficult to find a school without a mission statement. Staff development by then consisted almost entirely of the kind of training/motivation seminars that I would encounter a few years later working for Fortune 500 companies. Business jargon was all the rage. My first encounter with the school of education was when the dean gave us a talk on how Tom Peters and In Search of Excellence were going to revolutionize education.

For a while, I taught in a high school where the principal was known to say that he didn't like to base teacher renewal or promotion decisions on standardized test scores. He was careful not to say he wouldn't. That would have been a blatant lie. We knew he would make our lives miserable if we didn't teach to the test. He knew we knew it. But he maintained at least a vaneer of plausible deniability.

One particularly spineless history teacher spent about a month doing nothing but drilling facts that were likely to be on the test. No discussions. No writing assignments. No additional reading. No attempt to put the material into any kind of meaningful context. But his scores were good.

By the early Nineties, within less than a decade of the "Nation at Risk" report, states were starting to pass charter school laws. Pushes for merit pay and weakening tenure intensified. Faith in business as a source of answers for schools continued.

Education reform has proceeded in more or less a straight line for more than a quarter century without much that can be held up as a clear success. This isn't necessarily a damning criticism. Reformers like Fisman and Klein could honestly argue that the current state of education is mixed, not as good as it could be but not as bad as it would have been if steps had not been taken, or they could argue we have a classic case of half measures, that these reforms would solve our problems if fully implemented but in their watered down form they can do no good.

Both of these arguments are honest and defensible.

What they can't honestly do is imply that we are where we are because we didn't listen to them.

*Why per capita and not per student?

Ray Fisman and the Tierney Ratio

The Tierney Ratio (sometimes called the Tierney Test because people love alliteration) is a measure of journalistic mediocrity named for its frequent subject, John Tierney. You find the Tierney Ratio of an article by counting the number of words it takes to address all of the significant problems in the article, then dividing that by the article's word count.

As you might expect, Tierney Ratios vary greatly from author to author. The sorely-missed Olivia Judson maintained a TR of virtually zero while writing for the New York Times while John Tierney, a science writer with no appreciable background in or aptitude for science, routinely had observed TRs in excess of one or two. (it is possible that Judson was kept in the Op-Ed rather than Science section out of concern that she would unfairly lower the latter's average.)

The value of the Tierney Ratio is somewhat limited by its serious data censoring problem (analogous to this well-known example). Faced with articles and essays of sufficiently low quality, researchers are almost always forced to leave significant mistakes, distortions and fallacies unaddressed.

Which brings us back to Ray Fisman's recent column in Slate, which reaches an almost Hellmanesque level of inaccuracy. Getting a true TR on something like this is an extraordinarily tedious job so the readers who aren't into hardcore education wonkery might want to skip the next few posts. You'll know it's safe to come back when we start posting Daily Show clips again.

Desperately Seeking Suzanne (Null)

In Life in Hell, Matt Groening once asked if there was anything scarier than an open-mic poetry night. As a general rule, I have the same reaction to comment sections. There are exceptions (Andrew Gelman's site come to mind) but most of the time your chances of happening upon an intelligent and insightful conversation are better when you sit down between two strange drunks in an unfamiliar bar.

So you can understand why I initially skipped over the comments to Ray Fisman's recent post (if comments are usually less intelligent and well-written than the articles they accompany, just imagine the Stygian depths these would have to sink to in order to follow Fisman). Fortunately Joseph did brave the bottom of the web page and discovered that the comments here were actually better than the piece that inspired them.

The best of that very good crop were the entries was by Suzanne Null, who is (I believe) an education professor in the Northeast. [update, strike that last part. It looks like Suzanne is a fellow Westerner.] In this series of comments she takes down Fisman brick by brick:

Didn't Fisman's teachers ever teach him to conduct some research and check the validity of his sources (there is better and more recent information than the 1997 research he cited) before he publishes something? Virtually all of the information in this article has already been debunked. See Ravitch's copiously-researcherd "The Death and Life of the Great American School System" (particularly Chapter 9) and practically everything by Stanford's Linda Darling-Hammond. For example:

1) There is a great deal of evidence that better training helps teachers improve instruction (see research by Darling-Hammond and on the "Research" section of the www.nwp.org site). Teachers are "made" (not born) through training, professionally supportive school environments, and supportive communities. Experience makes a difference in teacher effectiveness (Ravitch 190) and one of the most major problems with the teaching profession is its high rate of attrition; many teachers leave the profession by their fifth year.

2) Despite what this article says about identifying "bad" teachers, we haven't yet found a reliable way to identify who the "bad" teachers are. Test scores are one-dimensional and subject to numerous validity and reliability issues (Ravitch 152-154). In addition, despite the claims made in this article, test scores can vary significantly by teacher from year to year because there is so much variation among the students in the teachers' classes. (Ravitch 185-186). A teacher who the tests identify as "high performing" one year might appear to be "low performing" the next.


3) The article insinuated that schools can "close the gap" simply by hiring the top quintile of teachers. This research comes from Gordon, Kane, & Stagler 2006; Hanushek & Rivkin (2004), and Sanders (2000), all cited by Ravitch (183-184). This has also been debunked because the learning gains cited in these articles don't persist over time (Jacob, Lefgren, & Simms 2008) and because of the general unreliability of the tests, particularly when used for the purpose of evaluating teachers, which was not the primary goals when most of these tests were designed.

4) The effectiveness of Teach for America (TFA) has been inconclusive (Rativich 188-191). For example, an extensive study by Darling-Hammond's found that TFA teachers "had a negative or non-significant effect on student achievement" (2005, cited by Ravitch 189). Thus "degrees from prestigious colleges" are also NOT a predictor of effective teaching. In any case, it is delusional to believe that the entire country can sustain the constant turnover of teachers that has characterized TFA (particularly given schools' current budgets for teacher pay) or that this level of turnover would be desirable for our students (Ravitch 190).

5) The research on the "cumulative effects" of attending NYC charter schools has been proven to be invalid. Charter schools are not all successful -- some post higher test scores than their comparative "public" schools and others post lower scores. When they have higher scores, it is usually because they take the students who chose to enroll or enter the lottery system. These students and their families tend to be more engaged with their education in general, and thus tend to perform better, no matter what the teacher does. Charter schools also take fewer students with special needs, such as Special Education students or second-language learners. When researchers have adjusted for these differences in their data pools, they have found no significant differences between charter schools and public schools (Ravitch 140 -143).

...

What's particularly worrisome and insidious about the author's arguments are that they will further harm students within our school system. If the "thought experiment" of abandoning teacher selection based on qualifications and teacher training is ever carried out in favor of allowing anyone to try to teach so that the "data" can winnow out the top 20%, it will mean that our students will bear the brunt of training and selecting teachers. They will be subjected to a revolving door of completely untrained teachers, and they will lose educational time and opportunities as they experience the steep learning curve that is present for teachers in their first two years. Our students deserve trained and experienced teachers; they don't deserve to be the guinea pigs that have to test out anyone who walks in off the street.
...

If we really want to overcome "mediocrity" in schools, we should focus on retaining the best teachers, giving them the professional freedom and support to do their jobs, and incentives for high performance, not just on tests, but on other measures of teacher success. Since I began teaching in 2000, I've watched many of the hardest working, most committed, and most motivated teachers leave. Those who stay are a few of the truly exceptional ones, and many of the ones who are happy to administer lectures and scan-tron tests and then go home. Teachers have few opportunities for professional advancement (aside from maybe becoming a principal), and few incentives to go "over and above" in their jobs. If we really want to improve education, our school SYSTEMS' tendency to support the mediocre and discourage (or even fire) the best is what will need to change. This change will require better working conditions, better support, more resources, smaller classes, and even better pay incentives for our hardest working and best-performing teachers.
...

I would add that the whole "martyr" or indolent "loser" dichotomy presented in the media's portrayals of teachers allows our society to evade responsibility for actually improving schools. If the best teachers are great because they CARE so much about their students and are willing to sacrifice so much, and if as the article says they are "born great," then they won't require smaller classes, better materials, more manageable work responsibilities, or higher pay. And if the worst teachers are indolent, then more money isn't going to help them anyway. The entire construction allows our culture to continue to alternately lionize and blame teachers while doing nothing that would actually help support teachers in their endeavors to help students learn.
...

Actually, the one strategy that's been proven to raise test scores is to winnow out the low-scoring students. This can be accomplished by re-drawing school attendance boundaries, creating "choice" or charter schools (which of course don't have the "resources" for Special Education students, second-language learners, or students with behavioral issues), or by "encouraging" the low-performing students to drop out or leave. The schools that have done this have been able to tout the "excellence" of their school management and teacher training, and their principals and superintendents have often gotten promotions and large pay raises.

So maybe our schools should all try that.
...
Just to clarify, this last suggestion was facetious. If our only way to "improve" our schools is to stop serving all of our students, is that a form of "success" that's worth having?
...

EB, I've particularly heard stories about nepotism and favortism from teachers in rural schools, so I know it happens. But many teachers' major fear about "performance based" pay is that it will be subject to the same dynamics. Even if teachers are evaluated solely on "data" such as test scores (which isn't a good idea for other reasons), it is very easy for principals to stack the deck against teachers they don't like by giving them the lower-performing students, making them change grades, or subjects, giving them unfavorable schedules, etc. I've already heard from some teachers I know in a rural area that principals will "drive a teacher out" by say, transferring them from fourth grade to first, only to then blame the teacher when test scores dip because the teacher hasn't had time to accumulate the practice and materials for the new grade level.

Many teachers are supportive of standards, accountability, and even incentive pay, but they want to be evaluated in fair and equitable ways.

Suzanne, if you've got a place you're posting on a regular basis, let us know and we'll add you to our blogroll. What you have to say deserves the widest possible audience.

A Partial N-space of Eduction Reform -- another preblogged footnote

If we are going to have an intelligent conversation about education (which at this point would be a refreshing change of pace), we have to start by thinking about the n-space. There are multiple dimensions that have to be considered here. As long as the debate fails to acknowledge them or approaches them in a sloppy way, the analyses will continue to be fatally flawed.

We could look at this on the level of classes or individual students, but in this case it probably makes the most sense to think of each school as representing a point in this multidimensional space. We assume these points are more or less fixed with respect to some of these dimensions (grade level, population density [rural/suburban/urban], demographics, region, etc.) but we like to believe that we can change the position of these points with respect to other dimensions (retention, discipline, standardized test scores, etc.).

Why is it so important to think in terms of this multidimensional space? Because there are few meaningful statements that are valid across these various axes. When Doug Staiger and Jonah Rockoff (here via Ray Fisman) made radical suggestions about teacher hiring policies, they based them on a study of arguably the two least representative school districts in the country. Even if the rest of the study were sound (rather than being a train wreck, but more on that later), the findings would be worthless for most of the country.

Worse yet, when you make a substantial change in educational policy, there is a wide range of relationships between the effects you see along different dimensions, including possible inverse relationships between retention and other measures of school performance (the fastest and most reliable way for a school to improve its performance is to get rid of the students it can't handle).

Even with the most careful of reasoning, the most clearly stated questions and the most closely examined assumptions, this kind of complex, multidimensional system can react to new conditions in dramatic, counterintuitive ways. If you approach it with the kind of sloppy thinking that has dominated the education debate, you are asking fate to do some very bad things.


[thanks to Wikipedia for the hypercube]