14What The Study Says In this study of 16 teachers in two primary schools in the Netherlands, researchers built on findings from previous studies to demonstrate that a thoughtfully designed professional development program can be “effective and sustainable, if certain conditions are met” (p. 772) in changing teachers’ knowledge, beliefs, perceived problems, and classroom practices. Study description Linda Van den Bergh, Anje Ros, and Douwe Beijaard designed a teacher professional development program to improve teachers’ knowledge, beliefs, perceived problems, and classroom behaviors related to student feedback during active learning. Questions The study focused on the short- and long-term effects of a professional development program aimed at improving teacher feedback during active learning on: Primary school teachers’ beliefs regarding feedback during active learning; The problems primary