SWBAT solve a problem in which the total and one part are known. SWBAT find as many 2 addend combinations for 9 as possible.

Explorations of combinations! Two missing addend games and a story problem, focusing on finding combinations of 9, what else could a 1st grade teacher want.

5 minutes

Using the new adaptation of the Start At/Stop At routine, that was introduced three days ago, have the students play a few rounds of the activity. Continue to play as time allows.

15 minutes

The purpose of this discussion is to continue to develop the understanding and use of the counting on strategy.

I start by giving each student a cup and seven cubes. I want to pose a few problems that came up in the previous days playing of this game.

*"Yesterday, we played What's Under the Cup? I want to talk about the strategies that you used for playing this game."*

I then pose a few scenarios like There are 7 cubes, three are 3 under the cup and 4 outside of the cup, who can explain how they figured out how many were under the cup? I want to keep the focus of this discussion on strategies that were used to find the missing addend and specifically on the counting on strategy. Watch the video on the section resource titled *Student Using Counting On Strategy*.

I find these conversations important because the students can be exposed to ideas and strategies from the discussion and knowledge of their peers.

The CCSS expect that students to attend to precision by communicating precisely to others and try to use clear definitions in discussion with others and in their own reasoning ( **CCSS.Math.Practice.MP6**). In this case the students are explaining to others how they are using the strategy of counting on to figure out the missing addend. The students are determining the unknown whole number in a subtraction equation by relating three whole numbers.

45 minutes

The students will be engaged with activities that focus on combinations of numbers.

1. 9 Rocks and Balls: Post a copy of the problem (see section resource) on the board or rewrite it on a piece of poster paper. ** Read the problem aloud and ask them to start with this activity**. This is similar to the 10 Rocks and Balls activity that the students worked on in a previous lesson.

2. How Many In My Hand?: This was introduced in a previous lesson.

3. What's In My Cup?: This was introduced in a previous lesson.

Each of these games incorporates CCSS 1.OA.1.D.8. By clicking on the above links, you can view the explanation and connection to this standard.

While Students are Working:

You should use the Center Time Observation Sheet (see section resource) and circulate amongst the class. Today's focus should be on how the students are solving the 9 Rocks and Balls problem. The checklist allows you to note what approach each child is using and their understanding with the concept of combinations for a given total. You can spend as much time as needed on the 1st activity with the students because tomorrow's Center Time will allow you to observe (with the same checklist) how they are doing with the counting on strategy (while playing the other two games).