Lesson objective: Apply the 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 if length measurements are accurate and determine which of the rules for measuring with length units apply to each worked example.

Key Concept students will use:

- Length measurements are only accurate if the length units and the object being measured are aligned.

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. Students will evaluate if worked examples have been measured with length units accurately and they will identify which of the rules for measuring with length units applies to each example.

**Key vocabulary: **

- accuracy/accurately
- 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)