Grounded in the trans-contextual model, the purpose of the present study was to examine the role of self-determined motivation in Physical Education (PE) on self-determined motivation in Physical Activity (PA), PA intention, and accelerometer-measured habitual PA behavior among high-school aged adolescents. A sample of 394 Spanish high-school students (211 males and 183 females; aged 12-16 years) participated in the present study. The outcome measure of PA was established using accelerometry, whereas motiva- tion toward PA and PE as well as PA intention were measured using validated questionnaires. Path analyses supported in part the central propositions of the trans-contextual model. Self-determined motivation in PE predicted the self-determined motivation in PA (β=.45, p<.001, R2=.26). Self-determined motivation in PA predicted PA intention (β=.51, p<.001, R2=.41). The predictive strength from PA intention to behavior was weak (β=.11, p=.011, R2=.21) with a statistically non-significant mediational model from self-determined motivation in PA via PA intention to PA behavior (β=.28, p=.231). This weak-to-non-significant relationship does not fully support the previous findings that have shown the feasibility of the trans-contextual model in charting the pathways from self-determined motivation in an educational context to behaviors in an out- of-school context.