Teachers, like all professionals, require ongoing professional development opportunities to improve their skills. This paper provides evidence on effective professional development characteristics and how at-scale programs incorporate those characteristics. The authors propose a standard set of 70 indicators—the In-Service Teacher Training Survey Instrument—for reporting on professional development programs as a prerequisite for understanding the characteristics of those programs that improve student learning. The authors apply the instrument to rigorously evaluated professional development programs in low- and middle-income countries. Across 33 programs, those programs that link participation to career incentives, have a specific subject focus, incorporate lesson enactment in the training, and include initial face-to-face training tend to show higher student learning gains. In qualitative interviews, program implementers also report follow-up visits as among the most effective characteristics of their professional development programs. The authors then apply the instruments to a sample of 139 government-funded, at-scale professional development programs across 14 countries. This analysis uncovers a sharp gap between the characteristics of teacher professional development programs that evidence suggests are effective and the global realities of most teacher professional development programs.