The results indicated that adolescent competence in terms of school engagement and achievement were influenced by students’ relationships with their teachers and their peers as well as by the capacity of the school environment to meet the adolescents’ psychological needs. Specifically, the findings revealed that school fit and engagement were mediators linking relationships with teachers and peers to students’ academic achievement. Thus, in order to engage students in learning, it is important that the school environment meet the students’ psychological needs for autonomy, relatedness, and competence, and that meaningful relationships with others are fostered. The findings are consistent with Self-Determination Theory and suggest that a strategy supporting teachers to maintain autonomy support for students could improve the school engagement and achievement of adolescents. Data were gathered from 324 students enrolled in grades 10 and 11 at 2 high schools in Queensland, Australia. Students completed a series of questionnaires assessing academic engagement and disaffection, teacher-student relationships, peer relationships, school achievement, and school fit. Structural equation modeling and bootstrapping techniques were used to analyze the data as these techniques allow for the detection of both direct and indirect effects. Additional research is needed to fully support the application of Self-Determination Theory to a model of school achievement and engagement. Figures, tables, references