This study examined whether contextual and personal motivational variables, taken from self-determination theory, could predict student cognitive and affective experiences in school physical education (PE), as well as participation in optional PE in the following school year. Structural equation modeling analysis with a sample of 302 British adolescents showed that need support provided by the PE teachers was related to student need satisfaction, which in turn predicted self-determined motivation. The latter predicted directly various motivational indices and indirectly future participation in optional PE. Furthermore, multivariate analysis of variance tests showed that those who opted for PE (n = 171), compared with those who did not (n = 131), reported more positive motivational experiences in the previous school year. The findings call for the promotion of self-determined motivation in PE in order to enhance student positive experiences and participation rates.