The present study examined the role of behavioral engagement and disaffection as mediators between self-determination and academic performance. Participants were 545 secondary students (53.4% girls) aged 12 to 19 years. Variables were assessed in the Spanish language classroom over a nine-month period. Students estimated their self-determination, and their teachers assessed student engagement, disaffection, and performance. Structural equation models corroborated the hypotheses: the types of self-determination differentially predicted engagement (R 2 = .39) and disaffection (R 2 = .24), and were progressively more adaptive the higher the autonomy; self-determination, behavioral engagement, and disaffection predicted performance (R 2 = .43); engagement and disaffection partially mediated the relationship from external regulation (β = -.097; p < .002; Confidence Interval = -.177, -.051), identified regulation (β = .109; p < .006; CI = .054, .165), and intrinsic motivation (β = .139; p < .002; CI = .086, .206) to performance. The implications of these findings for current theory and educational intervention are discussed.