Lesson objective: Measure fractional lengths on number lines and rulers.

This lesson helps to build procedural skill with identifying unit fractions on a number line (and ruler). The partitioning of number lines and rulers is used here to introduce the idea that fractional lengths are invariant. This work develops students' understanding that a length does not change if its position on a number line or ruler changes.

Students engage in Mathematical Practice 5 (use appropriate tools strategically) as they measure fractional lengths on both number lines and rulers.

**Key vocabulary:**

- align
- length
- number line
- partition
- ruler
- unit
- unit fraction