The purpose of this paper is to review recent work that ACER has been doing to improve the usefulness of evaluations of professional development programs. This work includes the development of research-based instruments to measure: the nature and quality of the processes used to promote teacher learning; the impact of programs on teacher knowledge, practice and student outcomes; the relationships between these process and impact measures. The paper is based on approaches developed as part of four recent evaluations of professional development programs. These include: three evaluations of the Commonwealth Government’s Quality Teacher Program, as implemented in three separate states: New South Wales, CEC Victoria and the Northern Territory; and a major research study funded by the Commonwealth Government investigating the links between professional development and student learning outcomes.