Grounded in Self-Determination Theory, the purpose of this study was to analyze how motivational processes within Physical Education classes can predict intention to participate in sport or physical activity outside of the school curriculum. Participants included 1,692 Spanish students aged 12-16 years (M = 13.34; SD = 0.76) who participated in Physical Education lessons at 32 secondary schools. Structural equation modeling was used for analysis, and showed that perception of basic psychological need (BPN) support from teachers predicted autonomous and controlled motivation through BPN satisfaction. Furthermore, autonomous motivation positively predicted enjoyment, perceived importance of Physical Education, and intention to participate in sport or physical activity outside of school. Controlled motivation negatively predicted enjoyment, and amotivation positively predicted boredom. Finally, enjoyment and perceived importance of Physical Education positively predicted intention to participate in sport or physical activity outside of what was required in school. Results emphasize the importance of school based Physical Education to promote sport and physical activity participation among adolescents.