Ninth grade on-track is predictive of high school graduation, more than race, socio-economic status, and prior achievement combined. Although initiatives characterized by an intense focus on the ninth-grade year are being increasingly implemented, research has not fully documented and tested mechanisms linked to improved outcomes. Using survey and transcript-level data and causal mediation analysis, this study tests the effects of students attending high teacher efficacy (self and collective—TSE and CTE) schools on ninth grade on-track in an urban school district in a northeast state in the United States. It further examines the extent to which ambitious instructional practices, defined as culturally relevant and transformative pedagogy, mediate the effects of TSE on ninth grade on-track and how levels of supportive school culture moderate these relationships. The findings indicate that urban ninth-graders attending schools with high TSE and CTE are more likely to be on track at the end of ninth grade. Additionally, the direct effect of students attending a school with high TSE was mediated by the level of ambitious instruction. We discuss implications for teacher education (TE) and professional development.