Lesson objective: Measure length with length units of the same-size that are aligned with no gaps and no overlaps.

This lesson helps to build fluency with measuring accurately with length units. The "Rules for Measuring with Length Units" are used and reviewed because these rules highlight the requirements for an accurate length measurement. This work develops students' understanding that length measurements are only accurate if the length units and the object being measured are aligned.

Students engage in Mathematical Practice #2 (reason abstractly and quantitatively) as they measure with length units and make approximations when the length units and the object they are measuring do not exactly align; Mathematical Practice #5 (use appropriate tools strategically) as they use length units to measure length; and Mathematical Practice #6 (attend to precision) as they work with the non-standard length units to determine the length of the object being measured. Students evaluate worked examples to determine if they have been measured accurately with length units.

**Key vocabulary:**

- accuracy
- alignment
- gaps
- length measurement
- length units
- overlaps
- same-size
- span

**Special materials needed:**

- non-standard length units (blocks, building cubes, paper clips)
- items to measure (e.g. strips of paper)