Teachers and researchers have known for decades that the use of storybooks can have a positive impact on students' experiences with mathematics. This article describes how first graders in an urban public school actively engage with mathematics by using the story "Bean Thirteen" as a context for developing number sense. This activity demonstrated support for students' active engagement with mathematical concepts by prompting movement through a sequence of problem-solving steps, encouraging imagination in mathematical thinking, helping the children make mathematical connections, and providing opportunities to demonstrate enthusiasm. A bibliography is included.