Lesson objective: Understand that the graph of a proportional relationship passes through the origin and increases linearly.

Students bring prior knowledge of graphing proportional relationships from 6.RP.A.3A. This prior knowledge is extended to finding the constant of proportionality on a graph as students use graphs to show proportional relationships. A conceptual challenge students may encounter is that a graph that is linear is not necessarily proportional.

The concept is developed through work with graphs, which shows the proportional relationship between the quantities.

This work helps students deepen their understanding of equivalence because the constant of proportionality is equivalent to the unit rate.

Students engage in Mathematical Practice 4 (model with mathematics) as they graph relationships and determine which relationships are proportional.

**Key vocabulary:**

- dependent variable
- graph
- independent variable

**Special materials needed:**