Children with attention-deficit/hyperactivity disorder (adhd) are characterized by persistent patterns of inattention and impulsivity-hyperactivity, besides deficits in other cognitive functions, such as processing speed, despite of not having been completely clarified. This study aimed to determine whether there are differences between children with and without adhd in reaction time and in intra-individual variability in reaction time (VRT). Using a quasi-experimental design, 474 children (209 with adhd and 265 controls) answered the aula test; nonparametric analyses were used. Results revealed that children with adhd combined subtype manifested a higher reaction time in targets and commission errors, while children with adhd combined and inattentive subtypes showed greater vrt than the control group. Evidently, the vrt is a key marker of ADHD.