This study aims to explore the relation between cognitive ability (using Wechsler Intelligence Scale for Children - Fourth Edition, Vietnamese version) and academic performance in students with symptoms of Attention-deficit/Hyperactivity disorder (ADHD). The results of analyses on 42 students indicated the significant correlation between cognitive ability and academic achievement in these students. The full-scale IQ was the strongest single predictor of achievements in Mathematics and Literature. Among the four main indexes, the Verbal Comprehension Index (VCI) was highly correlated with the achievement in Literature. Students with learning disorders were weak in Letter - Number Sequencing and Coding subtests. Other predictors for Mathematics and Literature performances will be identified and discussed.