Photographs offer teachers a way to collect and explore student work that might other wise go unnoticed or minimally examined. A teacher might use photographs to analyze students' strategies and work to promote future instructional practices that result in higher student achievement. As a tool, photographs document student understanding and enhance lesson planning by embedding assessment within instruction to provide the teacher with more than one data source. Photographs also provide documentation of a child's growing understanding of mathematics for teachers and families. Additionally, photographs have been identified as a way to improve teachers' noticing skills, specifically attending to, interpreting, and responding to student thinking. This article presents using photographs as a formative assessment tool.