In this article we give a systematic review of the nature and design of earlier research into the impact of instructional development in higher education. Studies are clustered on the basis of the level of outcome that was measured, meaning that another synthesis technique is used than in prior reviews related to the same topic. In addition, we address some questions related to the differential impact of initiatives with varied duration, format, or target group, because these questions were left unanswered in earlier reviews. The results of our review provide a guide to improve studies of instructional development in order to get more insight into the real impact at different levels (teachers' learning, teachers' behavior, the institution, and the students). Some evidence is found of the influence of the duration and nature of instructional development on its impact. (Contains 5 tables.)