Lesson objective: Understand that a rectangle can be partitioned into equal rows and columns to create an array.

Students bring prior knowledge of defining attributes of rectangles from 1.G.1 and 1.G.2. This prior knowledge is extended to partitioning a rectangle as students partition rectangles into equal rows and columns. A conceptual challenge students may encounter is understanding that each row and column in the rectangle must have an equal number of congruent squares.

The concept is developed through work with previous knowledge of arrays, skip counting, and repeated addition, which will allow students to partition a rectangle into equal rows and columns.

This work helps students deepen their understanding of equivalence because it is important for the groups of objects in each row and column of an array to be equal; a rectangle can be partitioned into rows and columns of same-sized, congruent** **squares.

Mathematical Practice 7 (Look for and make use of structure) is used in this lesson. As students compose arrays, they recognize that the array structure is a collection of rows or columns and that either can be seen as a unit.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they partition a rectangle into equal rows and columns of same size squares.

**Key vocabulary:**

- array
- columns
- equal
- partition
- rectangle
- rows