Maybe private schools get better results because they teach better….
Critics of school choice often argue that the reason private schools get better results is that they pick and choose their students, excluding those with disabilities. Now a State of Wisconsin study suggests that, "while the percentage of students in the voucher schools with disabilities is substantially lower than the disability rate in the public schools, it is at least four times higher than public officials have claimed." As well, the study points out that public schools have an incentive to identify students as disabled (because they receive additional funding for disabled students), while private schools have no such incentive. Indeed, many private schools are relucant to identify their students as disabled - because of the danger that the children will be stigmatized. This means that private schools may actually have an even higher percentage of students with special needs.
This was similar to the findings of a 2004 Canadian study, which found that at least 13% of Ontario schools serve exceptional students.