Current reforms in mathematics education have called for a stronger emphasis on the teaching and learning of algebra for all students at all grade levels. Succeeding in algebra can prepare students to learn and understand more advanced mathematics in the future. One topic in algebra—the equal sign—has received considerable attention in middle school mathematics because it is a fundamental concept to understand algebra. In particular, middle school is a vital transition for students to develop from arithmetical reasoning of elementary school to algebraic reasoning of secondary school. Although middle school students’ difficulties with the equal sign are well documented, to date, little is known about how to use GeoGebra—a dynamic and an interactive tool—to develop middle school students’ understanding of the equal sign. In this paper, we explore one GeoGebra dynamic worksheet focusing on comparing two functions of the equal sign with graphical and algebraic representations. We also describe how this GeoGebra dynamic worksheet is used to promote middle school students’ relational thinking of the equality.