An emerging consensus exists in the school reform literature about what conditions contribute to student success. Conditions include high standards for academic learning and conduct, meaningful and engaging pedagogy and curriculum, professional learning communities among staff, and personalized learning environments. Schools providing such supports are more likely to have students who are engaged in and connected to school. Studies show students with caring and supporting interpersonal relationships in school report more positive academic attitudes and values, and more satisfaction with school. These students also are more engaged academically. The study reported in this paper was guided by a reduced version of the Self-System Process Model developed by Connell. In this paper, optimal and risk thresholds for the Student Performance and Commitment Index (SPCI) and engagement are reported, and then data on how much engagement matters for later success in school are presented. Thresholds associated with teacher support also are presented with estimates of how much teacher support matters for engagement in school. (Contains 4 tables and 9 figures.)