Objective: The present study investigated executive functions in students with high functioning Autism (HFA) and students with educable Down syndrome (DS) with Normally developing students, by means of executive functions test (mental flexibility, short term and working memory) in a post hoc research.  Method: To fulfill the aim of the study, 15 male students with HFA, 15 male students with educable intellectual disability and 15 normally developing male students were recruited from educational services. The utilized research instruments in this study consisted of The 2^nd version of Gilliam Autism Rating Scale (GARS2), Wechsler intelligence Test, Wechsler direct and reverse memory test and Wisconsin Card Sort Test (WCST). To analyze the data, one-way ANOVA, Multivariate analysis of variances, Univariate Covariate, Multivariate Covariate and Bonforroni and Tukey Post-hoc were used. Results: Covariance analysis manifested that there was only statistically significant difference between high functioning Autism and control groups with respect to the mental flexibility index and perseveration. Moreover there was significant difference between Down syndrome and control group in short-term memory, while other comparisons did not reveal any significant difference between groups. Conclusion: The results indicated that students with HFA, due to having higher level of intellectual ability and acting at a level closer to normally developing students, showed impairment in the executive functioning. Therefore, this reduced the role of intelligence in the executive function level.