Many teachers in low- and middle-income countries lack the skills to teach effectively, and professional development (PD) programs are the principal tool that governments use to upgrade those skills. At the same time, few PD programs are evaluated, and those that are evaluated show highly varying results. This paper proposes a set of indicators-the In-Service Teacher Training Survey Instrument-to standardize reporting on teacher PD programs. An application of the instrument to 33 rigorously evaluated PD programs shows that 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. This paper then uses the instrument to present novel data on a sample of 139 government-funded, at-scale professional development programs across 14 countries. The attributes of most at-scale teacher professional development programs differ sharply from those of programs that evidence suggests are effective, with fewer incentives to participate in PD, fewer opportunities to practice new skills, and less follow-up once teachers return to their classrooms.