Lesson 11

The purpose of this lesson is for students to represent and solve Compare, Difference Unknown problems, in a way that makes sense to them.

In kindergarten, students compared quantities and answered “Are there enough?” questions. In this lesson, students interpret and solve Compare problems for the first time. Compare problems can be tricky for students because until now, they have only interpreted subtraction as taking apart or taking from. These problems require students to find the difference between quantities. In this lesson, students compare the number of connecting cubes in two towers so they can see the difference as they add or subtract cubes to make both towers have the same number of cubes.

As students explain their thinking, write equations to support connections between Compare problems and addition and subtraction. Building on the work of the previous section, include a box around the difference.

• Create a tower of 9 blue connecting cubes and a tower of 5 red connecting cubes.
• Each group of 2 needs 4 towers of 10 connecting cubes.

• Gather 1 red tower of 8 connecting cubes, 1 yellow tower of 3 connecting cubes, and a handful of yellow cubes.
• Each group of 2 needs 4 towers of 10 connecting cubes.

If you were to teach this lesson over again, what activity would you redo? How would your proposed changes support student learning?