Created as a partnership between the local school district, schools, community agencies, and university, the teacher residency program studied in this paper provided secondary teachers a clinically intensive pathway to learning to teach in urban classrooms, using co-teaching as the signature pedagogy. A current challenge related to teacher residencies is that few data exist connecting co-teaching to successful 8-12 student learning. This study explores the contributions of the urban teacher residency program's co-teaching apprenticeship to student success. The effectiveness of the apprenticeship co-teaching was measured using student achievement data (including both state and district assessments). The findings demonstrate that students in classrooms with Teacher Residents made growth in achievement and made more academic growth than students who were in the comparison classrooms. Findings from this study demonstrate that even as residents learning to become teachers work side by side with their mentors, 8-12 students in urban classrooms show promising learning gains.