Objective: The objective of this study is to elucidate the specific nature of attention and response inhibition deficits in three clinical groups: attention-deficit/hyperactivity disorder, oppositional defiant disorder, and high-functioning autism, as compared to children with a typical development. The analysis approached task performance dynamics as a function of time and the presence of distracting stimuli. Material and method: 108 children aged 7–12 years participated in the study – 21 diagnosed with oppositional defiant disorder, 21 with high-functioning autism, 19 with attention-deficit/hyperactivity disorder; 47 made the control group. The study employed the MOXO-CPT to evaluate attention and inhibition functions. Results: Pairwise comparisons of clinical groups with typically-developing children in their performance on the entire test indicated considerable differences between the control group and children with both oppositional defiant disorders and attention-deficit/hyperactivity disorder, but not between healthy subjects and children with autism. Performance profiles varied depending on the group, i.e. the type of disorder, and the level of the test, i.e. stimulus duration and intensity, but they were different for the particular studied aspects of attention and/or inhibition. High levels of similarity in functioning for all clinical groups were found in the measures of response accuracy, i.e. sustained attention and the speed of accurate response. The tendency to provide unnecessary responses and difficulties in complying with rules were found only in children with oppositional-defiant disorders. Impulsiveness rates increased over time in the attention-deficit/hyperactivity disorder group, fluctuated over time in autism, while in the oppositional defiant disorder group performance was stable over time, but worse than in the control group. Conclusions: The dynamics of attentional and inhibitory control in clinical groups differs considerably in comparison to typically-developing children. The most substantial differences between clinical groups are observed in the inhibition indices.