My son started meds very young much to my dismay but it did have the same response you are experiencing in your child at school. However, the rage and anger were horrible in the evening. At the time my son was taking Ritalin and I allowed it to continue for about 2 years only to read more and find out it can be a common side effect. We changed to Adderall and those symptoms almost entirely went away. He still has all the common anger and upset that can be associated with ADHD however now it is manageable and milder.