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 precision to the nearest minute as they read and write time. Students draw number line models that represent the minutes between multiples of 5, learning to count by fives and some ones as a strategy that they quickly apply to reading time to the nearest minute on the clock. In Lesson 4, students begin measuring time intervals in minutes within 1 hour to solve word problems. They reinforce their understanding of time as a continuous unit of measurement by counting forward and backward using the number line and the clock. Lesson 5 carries problem solving with time a step further. Students measure minute intervals and then add and subtract the intervals to solve problems.