Background: Physical activity (PA) improves outcomes, but disadvantaged children typically experience more sedentary behavior (SB). This study explored movement, executive function (EF) health, and academic achievement (AA) for economically disadvantaged kindergarteners. Methods: Children in 2 classrooms (n = 16; n = 7) wore wrist-based accelerometers to assess PA/SB during the school day. Independent t-tests and analysis of variance analyzed mean group differences in PA/SB and EF/AA, and correlations explored AA and EF associations. Results: The movement-based class spent significantly less time in SB compared to the contemporary class (t = 2.552, g = 1.115), made greater reading (t = -2.611) and math (t = 0.967) gains, and had better EF (t = 0.012). There were significant negative correlations between SB and math (r = -0.534) and reading (r = -0.592), but no significant relationships with EF. Implications for School Health Policy, Practice, and Equity: Schools should consider methods to decrease time spent in SB at lower-SES schools, which is financially feasible and less time-consuming than programs to increase PA. Conclusion: Decreased SB time was associated with better AA. More research is needed to determine whether interventions to decrease time spent in SB at school improve academic outcomes in disadvantaged children.