The relationship between intelligence and global adaptive functioning in young people with or without neurodevelopmental disorders

•Our study confirm findings from previous population-based research showing an association between IQ and global adaptive functioning.•However, this was only the case among children and adolescents without any neurodevelopmental problems.•Among children with autism, ADHD, language disorder and/tic disorder, IQ was not clearly associated with better global adaptive functioning.•This finding has implications for the interpretation of IQ test results in neurodevelopmental assessments and for policy decisions regarding access to services. Previous studies have shown an association between IQ and adaptive global functioning, i.e. how well a person is functioning in different domains of life. However, it is unclear to what extent such an association applies in children with neurodevelopmental disorders (NDDs). The study group consisted of 550 population-screened children assessed with the K-SADS, WISC-IV, and the C-GAS. Approximately half of the sample had been diagnosed with one or several NDDs (ADHD, autism, language disorder and tic disorder). A factorial ANOVA with IQ level and the presence of NDD was conducted, with C-GAS score as the dependent variable. Results revealed a significant interaction effect between IQ-group and NDD-status. In the non-NDD group (49% girls), higher IQ scores were clearly linked with better global adaptive functioning. Among children with NDDs (35% girls), however, higher IQ scores were not clearly associated with better functioning. Thus, the association between IQ and adaptive functioning were found to differ depending on the presence of NDD. These results have implications for the interpretation of IQ test results in neurodevelopmental assessments and point towards the importance of providing support based on an assessment of needs and functioning rather than scores from IQ tests.