Lesson objective: Understand that length can be measured with non-standard length units.

Students bring prior knowledge of ordering three objects by length and comparing the lengths of two objects indirectly by using the third object from 1.MD.A.1. This prior knowledge is extended to measuring length with non-standard length units as students choose non-standard length units and measure length using these length units. A conceptual challenge students may encounter is not understanding how to select and use these non-standard length units to find the length measurement of an object.

The concept is developed through work with measuring the length of paper strips, which demonstrates how length can be measured using paper clips, as non-standard length units, to measure each strip of paper.

This work helps students deepen their understanding of equivalence because the number of non-standard length units that are used to measure the length of an object are 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.

**Key vocabulary:**

- "guess and check"
- length measurement
- length units
- span

**Special materials needed:**

- non-standard length units (e.g. blocks, building cubes, paper clips, etc.)
- strips of paper for measuring length