Lesson objective: Extend understanding that length can be measured with non-standard length units when the length units are the same size, when they have no gaps between them, and when they do not overlap.

Students bring prior knowledge of measuring length from K.MD.A.1 and 1.MD.A.1. This prior knowledge is extended to measuring with accuracy with length units as students identify the rules for measuring with length units. A conceptual challenge students may encounter is not understanding how to apply the rules for measuring with length units (no gaps, no overlaps, length units need to all be the same size).

The concept is developed through examining worked examples, which provides students with the opportunity to evaluate if the rules for measuring with length units have been followed in order to ensure an accurate length measurement.

This work helps students deepen their understanding of equivalence because the number of same-size length units that span an object with no gaps or overlaps is equal to the length measurement of that object.

Students engage in Mathematical Practice #2 (reason abstractly and quantitatively) as they measure with non-standard length units and make approximations when the object being measured and the length units do not exactly align; Mathematical Practice #5 (use appropriate tools strategically) as they use non-standard length units to measure length; and Mathematical Practice #6 (attend to precision) as they strategically manipulate non-standard length units to find the length measurement of an object. Students evaluate worked examples of measurement with length units and determine how to address inaccurate measurement by employing one or more of the length measurement rules.

**Key vocabulary:**

- accurately
- 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)