In this interactive from APT, verify that equivalent linear expressions operate the same regardless of the value substituted for the variable. In the accompanying classroom activity, students use the interactive and then write real-world story contexts to match linear expressions and write expressions to match story contexts. They conclude by discussing ways to verify equivalence of expressions. To get the most from the lesson, students should be comfortable writing and evaluating linear expressions. This resource is part of the Math at the Core: Middle School Collection.