Introduction. Fluid intelligence is defined as the ability to reason, solve problems and adapt, while working memory is a temporary system for holding and manipulating information for complex tasks. Both factors are part of executive functions and are closely linked because working memory is fundamental for the reasoning and flexibility of fluid intelligence. Therefore, the aim of this study is to determine the level of the impairment of these variables in children with ASD, ADHD, or without neurodevelopmental problems, and to compare the groups.

Material and Method. To conduct the study, two questionnaires were assessed: the Raven’s Test and the WISC Arithmetic subtest. The sample consisted of 12 girls and 21 boys (M = 9.94; SD = 1.44) between 7 and 13 years old. Of these, 36.40% had no disorder, 36.40% had ADHD, and the remaining 27.30% had ASD. This was a quantitative study, and the data were analyzed using IBM SPSS statistical software.

Results. No statistically significant differences were found among the three groups on the Raven’s Test. However, significant differences were observed in the WISC Arithmetic subtest, where children with ADHD (M = 17.50; SD = 3.71) scored lower than the group without disorders (M = 24.09; SD = 3.21) (F = 7.309, p = 0.003, η² = 0.335). Although no statistically significant differences were found in the Raven’s test, we observed a large effect size (F = 1.861, p = 0.173, η² = 0.110), suggesting that significant differences might exist if we increased the sample size.

Conclusion. Despite the executive function impairments observed in individuals with neurodevelopmental disorders, significant differences were only found in the WISC Arithmetic subtest. This subtest evaluates quantitative reasoning ability and the mental manipulation of arithmetic problems, both of which involve working memory. A larger sample size is necessary to determine the differences between the distinct groups in the Raven’s test.