Lesson objective: Understand that length in inches can be estimated by comparing to benchmark objects - finger joints and dollar bills.

Students bring prior knowledge of estimating length from exploring standard units of measure in Grade 2. This prior knowledge is extended to estimation as students estimate the length of several objects. A conceptual challenge students may encounter is not understanding that estimation and measuring exactly are different.

The concept is developed through work with estimating the length of objects, giving students concrete benchmarks to estimate.

This lesson helps to build fluency with estimating length in inches. Finger joints and dollar bills are used here because they are about the length of an inch and six inches respectively. This work develops students' understanding that benchmarks can be used to estimate length.

This work helps students deepen their understanding of equivalence because objects used to estimate can be combined to estimate other the length of other objects.

Students engage in Mathematical Practice 5 (Use appropriate tools strategically) as they decide which benchmarks to use. Students can choose dollar bills, finger joints, or a combination of the two.

**Key vocabulary:**

- benchmark
- estimate