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…

States, programs, and schools have long focused on the inputs of teacher preparation--the rules for candidates and the preparation programs they attend--because inputs were thought to predict teacher effectiveness, and because they were often the best option available. But in the early 2000s, policymakers began trying to evaluate preparation…