Children, adolescents and adults with ADHD are easily distracted by stimuli in their environment. This can be any other important or irrelevant acoustic or visual stimuli. So ADHD is characterized by the inability to control what one pays attention to. The children with ADHD are not able to inhibit other stimuli or to stay focused to one task. Actually many ADHD children can focus on a very interesting task (hyperfocussing), but are not able to shift their attention focus in an appropriate way.

A typical problem for adhd children are "boring" tasks like doing homework or cleaning up their room. Usually any other stimuli (e.g. a bird outside the window, a dog barking next door, or a toy) will distract the child. Now the attention focus has completely changed, the old task is "off mind".