One important point is that there is a big difference between counseling a student out because they have low test scores and counseling them out because they are actively disrupting the education of their peers.The first issue here involves metrics. The idea that you should build a school system around a handful of test scores is one of the central tenets of the reform movement. Test scores are supposed to drive funding, contracts, allocation of resources, evaluations, bonuses, even terminations, but if you give certain schools more freedom to get rid of disruptive students the whole system breaks down.
Disruptive students not only take up time from the teacher that could be used in instruction; they also make it difficult for students to concentrate and tempt other others to act up. The result is that everyone's test scores go down.
By getting this student transferred you've not only raised the scores of an entire classroom of your students; you've lowered the scores of a comparable number of students in a public school in the same area. Since your school's evaluation, funding, and future contracts are dependent on your performance relative to other schools in the area, you can get a substantial double lift out of that single transfer.
And since public school to a large extent have to work with the students they are given, charter schools always win this one.