1. Are attention-related problems in the classroom (as measured by time on-task and on-task span) exacerbated in children with ADHD in specific class context conditions with respect to (a) specific class structures and (b) academic content area with inclusion of instructional transition periods? Our predictions were that children with ADHD will generally display lower levels of on-task and shorter on-task span and that whole class group teaching, highly academic lessons, and transition periods will challenge on-task behavior in all children, but particularly in those with ADHD. In statistical terms, we predicted a significant interaction between group and context conditions. Additionally, we took into account the possible confounding effects of frequently co-occurring problems associated with oppositional defiant disorder (ODD) and academic underperformance in the ADHD group.