The work of this lesson builds on work from kindergarten when students composed and decomposed numbers in more than one way and represented these decompositions with their fingers, connecting cubes, two-color counters, drawings, and expressions. Students revisit Put Together/Take Apart, Both Addends Unknown problems through a game in which they decompose a total into two addends.

During the Synthesis of each activity, students are invited to make sense of equations that represent the part-part-whole relationships in the game. Students may also begin to represent their thinking with equations, although this is not expected at this time. The focus of the discussion in the lesson should be on making sense of the addends, their relationship to the total, and their meaning in the context of the game. These conversations will help students as they make sense of and solve Put Together/Take Apart, Addend Unknown problems in the next lesson.

What evidence have students given that they understand they can add in any order? What evidence can you look and listen for as students develop their understanding of the commutative property?