Every year, new teachers collectively spend about $4.8 billion on their training requirements, nearly all of which goes to teacher preparation programs. Unfortunately, it is unclear whether that is money well spent. Despite decades of research and ongoing calls to improve the quality of teacher training, we still do not know how to sculpt an effective teacher preparation program. In this report, the authors argue that a new approach focused on rigorous, actionable research is critical to driving improvement in teacher preparation. To create that body of research, the field needs: (1) systems that link completer performance data to preparation programs, make those data publicly accessible, and maintain individual privacy; (2) research methods that use those data to produce actionable strategies and effective practices to improve program design; and (3) policies that incentivize programs to evaluate the effectiveness of their model and adopt new, evidence-based practices. The end result should be a body of rigorous research that explores a multitude of possible improvement strategies, testing which components of program design are effective, for whom, and under what circumstances. Until those pieces are in place, the quality of teacher preparation will remain stagnant. The authors make several interrelated recommendations to authentically improve teacher preparation that are the shared responsibility of researchers, preparation programs, and state and federal policymakers.