Attention deficit hyperactivity disorder (ADHD) is one of the most commonly diagnosed mental health disorders in children. It is characterized by difficulty paying attention, excessive activity, and impulsivity that is inappropriate for the child’s age. With ADHD, these symptoms are present in multiple settings such as school, home, or with friends and cause significant impairment in functioning.
One question that often comes up is whether ADHD affects performance on IQ tests. IQ (intelligence quotient) tests are standardized measures designed to assess intellectual abilities like reasoning, problem solving, and knowledge. Parents and teachers often wonder if the symptoms of ADHD like inattention or hyperactivity might lower a child’s test scores and inaccurately reflect their true intelligence.
In this article, we will review what research says about the impact of ADHD on IQ and academic achievement tests. We will discuss factors that can mediate the relationship between ADHD and IQ scores. Finally, we will provide recommendations for properly assessing children with attention difficulties.
The impact of ADHD symptoms on IQ scores
Several studies have compared the IQ scores of children with and without ADHD to shed light on this issue. The findings have been mixed.
Some studies have found lower full-scale IQ scores in children with ADHD compared to peers:[1]
- In a meta-analysis of 15 studies, children with ADHD scored on average 9 IQ points lower than children without ADHD.
- The largest study followed 5,718 children and found those with ADHD had full-scale IQ scores that were 2.5 points lower on average.
- The difference was largest for verbal IQ scores, with children with ADHD scoring 5.5 points lower on average than their peers.
However, other studies have not found significant differences in IQ scores:[2]
- Several studies report average IQ scores in the ADHD group were within the normal range and not meaningfully different from the control group.
- One study of 1,381 youth found no significant difference in full-scale, verbal, or nonverbal reasoning IQ scores between children with and without ADHD.
Overall, while some studies do show modest reductions in IQ scores among children with ADHD, the average scores still fall well within the normal range. The deficits seen are not severe enough to meaningfully distinguish the groups.
Factors that influence the relationship between ADHD and IQ
There are several factors that may influence the relationship between ADHD symptoms and IQ scores and contribute to the mixed findings:
- ADHD subtype – Studies indicate differences may exist between the predominantly inattentive and hyperactive-impulsive subtypes. Greater deficits in IQ appear more likely among the inattentive subtype.[3]
- Comorbid conditions – Co-occurring learning disabilities or psychiatric disorders may have more of an impact on IQ than ADHD alone.[4]
- IQ test used – Some measures like digit span or coding/symbol search are more affected by attention problems than verbal IQ tests.[5]
- Age and gender – The relationship between ADHD and IQ may differ depending on age group and between genders.[6]
- ADHD severity – More severe ADHD symptoms are associated with greater reductions in IQ scores.[7]
- Treatment status – Studies indicate medication for ADHD may improve scores and lessen differences versus peers.[8]
This suggests the disorder itself may not directly cause IQ reductions. Instead, factors like inattention during testing, IQ measurement used, and comorbid disorders may influence results.
ADHD and academic achievement
While the impact on overall IQ is modest, ADHD often impairs children’s academic achievement and test performance:
- Children with ADHD are more likely to perform below grade level and score lower on standardized tests of math and reading.[9]
- One study found 41% of children with ADHD repeated a grade in school compared to 8% of peers without ADHD.[10]
- ADHD is associated with lower school grades and poorer scores on state-mandated achievement tests.[11]
- Impairments in reading, writing, and mathematics are common among children with predominantly inattentive ADHD.[12]
ADHD symptoms like difficulty sustaining attention, following instructions, and completing work can negatively affect schoolwork habits and test taking skills. Children may also miss crucial concepts and learning opportunities due to inattention, disruptive behavior, or missing school, affecting knowledge acquisition needed for testing.
Recommendations for assessing children with ADHD
Based on the research, ADHD has a modest effect on IQ scores on average and a stronger relationship with academic achievement. There are recommendations psychologists make to ensure testing accurately captures a child’s abilities:
- Use rating scales to understand the child’s symptom severity and areas of impairment.
- Assess for co-occurring conditions like learning disabilities which may have greater impact on scores.
- Choose an age-appropriate IQ test with no or minimal timed portions if possible.
- Make accommodations like frequent breaks, separate or private testing rooms, and allowing movement during testing.
- Compare results to parent/teacher reports of functioning at school and home.
- Re-evaluate with testing after beginning ADHD treatment to assess for improvements.
- Interpret results cautiously as a snapshot rather than sole indicator of intelligence.
Proper diagnosis and management of ADHD symptoms is crucial to reduce the impact on learning and improve academic success. Multimodal treatment plans including school supports, behavior therapy, academic interventions, and medication when appropriate can help children with ADHD thrive.
Conclusion
While study findings are mixed overall, most research shows ADHD has a minor negative association with IQ scores. However, average scores still fall within the normal range. It is likely not the disorder itself but rather factors like inattention during testing, presence of comorbid disorders, and which IQ tests are used that influence results.
ADHD often has a greater impact on school and academic achievement test performance. Symptoms can impair learning, test-taking skills, and knowledge acquisition. But with proper accommodations, effective ADHD treatment, and a multimodal approach, children with ADHD can successfully demonstrate their abilities intellectually and academically.