Many teachers are concerned about providing feedback to students in ways that support student learning. Five middle school teachers, part of the Classroom Assessment Project to Improve Teaching and Learning (CAPITAL), explored classroom-based assessment in science. The teachers experimented with different approaches to assessment and met regularly with other teachers and researchers to share and discuss their evolving practices. The CAPITAL teachers moved toward a more complex understanding of the nature of feedback, the purposes for feedback, and the roles feedback could play in their classroom.