This research report examines the dramatic turnaround of the Mildred Avenue School in Mattapan, which won EdVestors' 2017 School on the Move Prize. We teamed up with EdVestors to investigate the role of teacher leadership and labor-management collaboration in driving rapid school improvement. In 2013, the Mildred was a school in crisis. Academic performance, as measured by the MCAS, was among the lowest in the Commonwealth. Average principal tenure was just 18 months, and shifting priorities contributed to poor school climate among students and staff. Five years later, the Mildred is a Level 1 school, the highest accountability category designated by the Massachusetts Department of Elementary and Secondary Education. The school has achieved dramatic gains in both school culture and academic achievement with learning characterized by a focus on academic rigor. This report studies the unique Boston Public Schools/Boston Teachers Union collaboration that allowed teachers to form an intervention team, charting the school's improvement plan. It concludes with lessons learned regarding the sustainability and replicability of the Mildred's approach. [This report was co-produced by EdVestors.]