This paper describes students' interactions with dynamic diagrams in the context of an American geometry class. Students used the dragging tool and the measuring tool in Cabri Geometry to make mathematical conjectures. The analysis, using the cK[cent sign] model of conceptions, suggests that incorporating technology in mathematics classrooms enabled a measure-preserving conception of congruency with which students' could shift focus from shapes to properties. Students also interacted with dynamic diagrams in a novel way, which we call the "functional" mode of interaction with diagrams, relating outputs and inputs that result when dragging a figure. Students' participation in classroom interactions through discourse and through actions on diagrams provided evidence of learning using tools within dynamic geometry software.