In interesting read. https://www.edweek.org/ew/articles/2016/04/20/number-of-us-students-in-special-education.html
After years of steady decline, the nationwide count of school-age students covered under the Individuals with Disabilities Education Act has shown an upswing since the 2011-12 school year based on the most recently available federal data, driven by rapid growth in such disability categories as autism. Students with specific learning disabilities such as dyslexia have been, and remain, the largest group of those covered under the IDEA.