Stimulant medications are an effective treatment for Attention-Deficit/Hyperactivity Disorder (ADHD). In the classroom, parents and teachers say that medications like methylphenidate (MPH) can reduce symptoms and improve behavior. Although stimulants have been in use for decades to treat ADHD in school-aged children, just how they work hasn't been clear. But the results of a new study are filling in critical gaps about the role of improved cognitive functions.