The purpose of this lesson is to review finding the constant rate of change of a linear relationship represented with a graph. It connects to concepts learned in grade 8, such as rate of change and slope. The work is scaffolded and additionally gives students an opportunity to revisit interpreting function notation. In the associated Algebra 1 lesson, students apply the idea of average rate of change to exponential functions. In each activity, students are asked to interpret function notation and graphs in terms of the context they represent, which gives them an opportunity to reason abstractly and quantitatively (MP2). When students interpret and see as an object that has a value, they have an opportunity to notice and make use of structure (MP7).