Joseph has an interesting link to a comparison of test scores of fifteen-year-olds in different countries. I recommend you go by and take a look. It has some interesting stuff, but what caught my eye was what wasn't there. I couldn't find a complementary break-down for any other age group.
After bad metrics, I think the worst problem in educational research may be the inappropriate aggregation of primary and secondary education. If there was ever a case where two populations should be treated separately it's here. The two systems face different problems of different severity that respond to different solutions.
I'll try to follow up with some specifics later, but in the meantime, when you hear someone making a blanket proclamation about our schools, remember that about the only meaningful statement you can make that's true about primary and secondary schools is that the teachers in both are about to get screwed.