Lesson 1

The purpose of this lesson is for students to understand the structure of the number line and learn how whole numbers can be represented on the number line with tick marks and points.

In a previous unit, students learned about standard length units. They created their own rulers by iterating centimeter cubes and used their understanding of length units to measure the length of objects with rulers, meter sticks, and other tools. Students interpreted the scale of line plots and created their own line plots by relating their structure to the length units on measurement tools.

In this lesson, students learn about the number line, a diagram that represents numbers as lengths from 0 using equally spaced tick marks or points, and learn how to locate and represent whole numbers on the number line. Students are introduced to the idea of using a point to represent specific numbers on the number line. Students build on their experiences with measurement to construct a number line to represent numbers within 20. They learn that unlike a linear measurement tool or a line plot, the unit intervals on a number line do not correspond to a specific unit of measure. In the lesson synthesis, students consider how number lines with different unit intervals can be used to represent the same numbers and relationships.

• Each student needs a sentence strip or a 24–30 inch rectangular strip of paper.
• Each group of 2 students needs access to assorted objects that can be used as a length unit to construct number lines (base-ten blocks, inch tiles, paper clips, large erasers, small sticky notes).

In a previous unit, students learned to measure lengths using standard length units. How does this understanding help students understand the structure of the number line?