Students are introduced to rectangular prisms as they begin to informally use the structure of rectangular prisms to find the number of cubes in the prism. Throughout the course, assume all references to rectangular prisms, including images, are referring to right rectangular prisms.

In previous grades, students learned to measure area by counting unit squares, decomposing a rectangular region into rows and columns, and multiplying the number of unit squares in a row by the number of rows or the number of unit squares in a column by the number of columns. Similarly, in this lesson, students make use of the layered structure in a rectangular prism to count the unit cubes in a more systematic way (MP7). Students will have many opportunities to count the number of unit cubes in rectangular prisms in upcoming lessons, before the introduction of formulas later in this unit.

Math Community
Tell students they will have a chance to revise their math-community ideas at the end of this lesson. As they work today, students should think about actions that might be missing from the current list.

What did students understand about the volume of a solid object as they came into the lesson? In what ways did their understanding of volume change upon completing the lesson?