Background: Acute physical activity breaks lasting 10--60 min have been related to positive effects on student focus and academic performance. The aim of this study was to evaluate the impact of repeated brief physical activity-infused academic lessons (1-5 min) on student retention and on-task behavior. Methods: One class from each K-2 grade level (N = 114) was randomly assigned to the control or experimental condition. Teachers introduced two health and science lessons lasting no more than 5 min every day for six weeks using the 1-Minute Energizer (experimental) or sedentary equivalent (control) curriculum. Student knowledge and behavior was assessed pre- and post-intervention with curriculum-specific oral quizzes and classroom observations. Results: Improvement in quiz performance with the intervention (+80.5 ± 12.4%; p < 0.001) was not different between groups (F(1, 89) = 0.05, p > 0.05) despite greater lesson time in control classrooms. Experimental students exhibited fewer disruptive behaviors (DB) and spent more time on-task (OT) post-intervention (DB: F(1,89) = 10.72, p = < 0.01; OT: F(1,89) = 5.56, p < 0.05). Conclusions: 1-Minute Energizers are an effective instructional tool for increasing health and science knowledge with the added benefits of improving student focus and providing more opportunities for physical activity participation.