From the National Center for Policy Analysis:

A growing body of evidence indicates that much of the tremendous growth in special-education programs across the United States is the result of financial and other incentives, rather than a true increase in disabilities, say Marcus A. Winters and Jay P. Green [sic], both senior fellows with the Manhattan Institute. They also point to new research that suggest that school vouchers targeted to disabled students could reduce this artificial growth, saving taxpayers money and keeping kids from the sting of being mislabeled as disabled.