This study explored the use of classroom physical activity (PA) in secondary science rooms. To accomplish this, semistructured interviews were conducted with secondary science teachers (n = 11). Interviews were based on the constructs of the social-ecological model. Most teachers reported using classroom PA in some form—in-class breaks, outdoor activities, and curriculum support. Teachers used classroom PA to improve academic and behavioral outcomes of students. They had varied perceptions regarding collegial support of classroom PA, but mostly felt supported by administrators. Teachers reported being unaware of their district’s and the state department of education’s beliefs about classroom PA. Overall, factors that negatively influenced classroom PA use tended to be within the interpersonal, organization, and policy levels of the social-ecological model, while factors that positively influenced classroom PA use tended to be within the individual level.