Background: Physically active lessons have not often been assessed with randomized controlled trials. Aims: Evaluate the effects of the "Virtual Traveller" (VT) intervention delivered using classroom interactive whiteboards on physical activity, on-task behavior, and student engagement. Methods: Participants were 219 children aged 8 to 9 years from 10 schools in Greater London, assessed in a cluster-randomized controlled trial between March 2015 and May 2016. For 6 weeks, intervention children received 10-minute VT sessions three times a week during math and English lessons (VT group: n = 113). Children in control schools received regular teaching (COM group: n = 106). Outcomes were school-day, weekend-day, and lesson-time sedentary behavior (SB), light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA), and on-task behavior and student engagement, assessed at baseline (T0), 2 weeks (T1), and 4 weeks (T2) during the VT intervention and 1 week (T3) and 3 months (T4) postintervention using multilevel modeling. Results: VT pupils engaged in significantly more school-day MVPA at T1 only, with no other significant differences between groups in overall school-day or weekend-day activity. VT pupils engaged in significantly less SB and more MVPA during lesson time than COM pupils. More on-task behavior was shown in VT pupils than COM pupils but there was no difference in student engagement. Discussion: VT reduced sedentary behavior and increased physical activity during lesson time but not across overall school or weekend days. VT improved on-task behavior but had no effect on student engagement. Conclusion: Physical activity can be integrated into teaching using interactive whiteboards with no detriment to educational outcomes.