 Overall , studies have shown that people with ADHD tend to have lower scores on intelligence quotient ( IQ ) tests . The significance of this is controversial due to the differences between people with ADHD and the difficulty determining the influence of symptoms , such as distractibility , on lower scores rather than intellectual capacity . In studies of ADHD , higher IQ ’ s may be over represented because many studies exclude individuals who have lower IQ ’ s despite those with ADHD scoring on average 9 points lower on standardized intelligence measures . As a result , we may have less of an accurate understanding of ADHD . 
