Earl Oremus, headmaster at Marburn Academy in Columbus, said that hyperactive and impulsive characteristics of ADHD are usually very evident in toddlers. "The disorganization and lack of focus are usually somewhat visible before school-age, but become much more visible when school expectations of managing focus and organization become important," he said.

During ages 3 through 6, children begin to slowly increase their attention spans and ability to sit still for short to moderate periods of time. Kathryn H. Leugers, Psy.D., M.B.A. with Meers, Inc. Consulting Psychologists in Columbus, said that hyperactive and impulsive symptoms often become apparent in early childhood during pre-school, kindergarten or early elementary school, while the inattentive symptoms sometimes are not noticed until elementary school or middle school years. "Sometimes children or teens that are either strong academically or struggle academically due to learning differences or other psychological issues may have ADHD that is not detected until a bit later on in development."