In close to two decades, there has never been a case of dyslexia at Sudbury Valley. No one knows exactly why. The cause of dyslexia, the nature of dyslexia, the very existence of dyslexia as a true functional disorder are matters of great dispute. Some authorities say that as much as 20% of the populations suffers from this alleged disorder.

http://www.ablechild.org/education/the%20other%20r's.htm (copy & paste)