This chapter describes the use of a computer-based animation and manipulatives to support learning and communication of mathematical thinking in a fourth-grade classroom. The educational animation called Overruled, part of the Math Snacks project (mathsnacks.com), was utilized to address the concept of length units. The animation describes a story in which the king and the queen from two different kingdoms (Kingopolis and Queentopia) fell in love and wanted to unite their territories by constructing a bridge. Engineers from each kingdom were responsible for building their side of the bridge. However, each kingdom has its own length unit. Authors follow research based recommendations to use the Overruled animation in mathematics activity with fourth-grade students.