In the last three decades, special-education programs in the United States have grown at a tremendous pace. Much of this growth reflects a growing incidence of students diagnosed with the mildest form of learning disability, called a Specific Learning Disability (SLD), and thus the hardest to distinguish from an ordinary cognitive deficit. Between 1977 and 2006, the proportion of public school students diagnosed with SLD trebled, from 1.8 percent to 5.6 percent. By the end of that period, 40.7 percent of all students enrolled in special education had been identified as having an SLD. A limited but growing body of research suggests that financial and other incentives may be responsible for a portion of these increases. The question examined in this report is whether special-education voucher programs change the likelihood that students will be diagnosed with an SLD. Voucher programs allow disabled students to attend a private school, which receives payments in the form of full or partial tuition that would have otherwise been directed to the transferring student's public school. Special-education voucher programs appear to reduce a local public school's financial incentive to diagnose a marginal student who is merely struggling academically as suffering from an SLD by offering him the chance to leave the public school, enter a private school, and take all of his funding with him. (Contains 5 tables and 10 endnotes.) [This paper was supported by the Walton Family Foundation.]