Lesson objective: Counting by twos or pairing objects to determine if a set of objects is even or odd.

Students bring prior knowledge of decomposing numbers into pairs in more than one way from Kindergarten, Unit 10, K.OA.3. This prior knowledge is extended to even and odd numbers as students count by twos or make pairs to determine if a number is even or odd. A conceptual challenge students may encounter is realizing that in order to claim a number is even, the equal pairs must consist of only two items, i.e., three equal groups of three is nine, and nine is odd.

The concept is developed through work with pairing up circles, which supports student understanding that a number is considered even when you can decompose it into pairs with no leftovers. It also sets the stage for the use of arrays in understanding the foundations of multiplication.

This work helps students deepen their understanding of numbers because decomposing a number by counting by twos or pairing objects will shed light on determining the difference between an even and odd number. An odd number will always have an object left over.

Students engage in Mathematical Practice 4 (Model with mathematics) as they apply what they know about even and odd numbers to solve within a context of counting beads. Students also engage in Mathematical Practice 7 (Look for and make use of structure) as they decompose the number 20 to explore skip counting and pairing objects to find even numbers.

**Key vocabulary:**

- addend
- decompose
- even
- odd
- pair

**Special materials needed:**

- Counters (if students need to model the numbers before drawing)