Lesson objective: Estimate length by measuring objects to the nearest whole, half, or fourth inch.

Students bring prior knowledge of measuring with precision to the nearest whole, half, and fourth inch from earlier in this unit. This prior knowledge is extended to situations where precision is not needed as students report lengths to the nearest whole, half, and fourth inch. A conceptual challenge students may encounter is understanding when precision is needed versus when estimation is sufficient.

The concept is developed through work with rulers, which can be used to help students visualize the nearest whole, half, and fourth.

This work helps students deepen their understanding of equivalence because lengths can be reported in different ways even though the physical length of an object does not change.

Students engage in Mathematical Practice 2 (reason abstractly and quantitatively) as they decide how to round fractional lengths to the nearest whole, half, or fourth.

**Key vocabulary:**

- approximate
- estimation
- fourth inch
- half inch
- quarter inch
- whole inch

**Special materials needed:**

- rulers (with partitions to at least the half inch)