Lesson objective: Understand that skip counting and repeated addition strategies can be used to find the total number of a set of objects in an array.

Students bring prior knowledge of skip counting by twos or fives from 2.NBT.2 and their work with addition and subtraction from 1.OA.7. This prior knowledge is extended to their work with arrays as students use skip counting and repeated addition as strategies to find the total number of objects in an array. A conceptual challenge students may encounter is fluently skip counting.

The concept is developed through work with arrays, which allows students to use skip counting or repeated addition to create arrays because there is the same number of objects in each row and column.

This work helps students deepen their understanding of number because arrays can be counted with repeated addition or skip counting; skip counting and repeated addition can be used to find the total number of objects in an array because there is the same number of objects in every row or column.

Students engage in Mathematical Practice 2 (Reason abstractly and quantitatively). Students will make connections between equal groups of objects and arrays and the concept of adding equal addends.

**Key vocabulary:**

- addends
- addition
- array
- columns
- equal
- objects
- repeated
- rows
- skip counting
- total

**Special materials needed:**