Lesson 1 is an exploration in which students use stopwatches to measure time as a physical quantity. Lesson 2 builds students’ understanding of time as a continuous unit of measurement. They learn to draw the model, labeling hours as endpoints and multiples of 5. Through this work, students recognize the analog clock as a portion of the number line shaped into a circle, and, from this point on, use the number line as a tool for modeling and solving problems. Lesson 3 increases students’ level of