The concepts of angle and angle measure have been acknowledged as difficult for elementary school students to grasp (Strutchens, Martin, and Kenney 2003). The Wedge activity (Browning and Garza-Kling 2009; Van de Walle 2004; Wilson 1990) can provide an opportunity for students to examine their understanding of angle measurement and to rethink what it means to measure angles. The activity can be used to support a learning trajectory for students' development of the angle-measurement concept. Teachers who can recognize where their students are on a learning trajectory for a topic can make effective decisions about how to move students along the trajectory to the ultimate learning goal. (Contains 4 figures.)