[Pete Zicato]

Aaron Donnell, an allergist and pediatrician at Children's Memorial Hospital and Illinois Masonic Hospital, said that if parents have questions about attention-deficit disorder, he tells them that skin- or blood-testing won't help, but they can try removing gluten, sugar, dyes or preservatives from the child's diet. "At least half get some improvement by adjusting their diet," he said.

From this article in the Chicago Tribune. Sounds like a significant statistic to me.