Lesson objective: Understand that when counting a collection, each item must be counted once and only once.

Students bring prior knowledge of rote counting within 20 from K.CC.A.1. This prior knowledge is extended to counting with one-to-one correspondence as students practice counting a collection of items. A conceptual challenge students may encounter is understanding that each item must be counted once and only once.

The concept is developed through work with blocks, which help students connect numbers to the objects being counted.

This work helps students deepen their understanding of number because counting objects is a foundational skill that strong number sense will build upon.

Students engage in Mathematical Practice 6 (Attend to precision.) as they count a collection of objects carefully, making sure to count each object once and only once.

**Key vocabulary:**

- collection
- counting
- eight
- five
- four
- nine
- object
- one
- seven
- six
- ten
- three
- two

**Special materials needed:**

- 1 bag (per partnership)
- 1 red block (per partnership)
- 2 blue blocks (per partnership)
- 3 purple blocks (per partnership)
- 4 yellow blocks (per partnership)
- 5 green blocks (per partnership)
- five frame and block matching cards (provided)