In previous lessons, students represented and solved each of the three types of Put Together/Take Apart problem types. They shared and compared different ways to represent and solve these problems. In this lesson, students compare the different Put Together/Take Apart problem types with a focus on describing what is unknown. Look for the ways students continue to progress from directly representing all of the quantities in a problem to using objects and drawings to represent counting strategies, including counting on from one addend to the total or counting back from the total to a known addend. During the second activity, students have an opportunity to compare counting on and counting back strategies and begin to consider how they can use the relationship between addition and subtraction to solve problems.

This lesson lays the foundation for understanding subtraction as an unknown addend problem. This concept will be explored further in Section C.

Students do not need to master representing and solving these problem types until the end of grade 2. So, the important part of this lesson is that students can make sense of the story problems and make sense of counting strategies.

What opportunities are you giving students to reflect on their understanding of the mathematical content?