Lesson objective: Apply rules for measuring with length units to measure length accurately.

This lesson provides an opportunity for students to apply their knowledge and understanding of the rules for measuring with length units to a mathematical situation. Students are asked to evaluate worked examples and determine if they have been measured accurately according to the rules for measuring with length units (no gaps, no overlaps, length units must all be the same size).

Key Concept students will use:

- The length measurement is the number of same-size length units that span an object with no gaps or overlaps.

Skills students will use:

- Students will evaluate worked examples of strips of paper measured with length units.
- Students will determine if the strips of paper were measured accurately with length units.
- Students will identify the length measurement rule that could be used to accurately measure the length of an incorrectly measured worked example.

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; Mathematical Practice #6 (attend to precision) as they strategically manipulate non-standard length units to measure the length of a given object or distance. Prompt students to remember to make an approximation, or guess, about the length of the object/ distance and check their guess by doing the actual measurement work. Students are prompted to analyze worked examples and ask themselves, "Is this example measured accurately? What can be done to measure it accurately?"

**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)