A diagnosable disorder should bring a bonus on your voucher. Of course, this means that you'll need a vast special ed bureaucracy to set standards and diagnose. But we already have it, because school districts get extra money for special ed. I'm not sure how much new administrative overhead this would entail.
This article available online at:
http://www.theatlantic.com/business/archive/2008/09/vouchers-what-to-do-about-special-ed/4092/
