Have a group of approximately eight students stand in front of the room. Ask the class how many students are at the front. Divide the group into two smaller groups and ask the class how many students are at the front now and how do they know. Explore the different ways that we could partition the larger group.
Look For …
Do students:

notice doubling a number is counting by twos?
. Recess Lineup
Students should have access to counters or cubes as well as paper and markers. Present the following problem to students: "At recess time today, I am going to have you line up in two lines. How many students are in each line for our class?" Have them actually form the two
lines as an example. The teacher should stand in the lineup if there is an odd number of students present. Then repeat this for students, using different even numbers in the class; e.g., 22, 24, 20, 16, 10. Have students draw pictures and write an addition sentence to describe what they drew. Draw attention to the fact that two 9s is the same as nine 2s, and so on.
3. Ten Felt Markers
Have 10 green and 10 red felt markers (or make 10 red and 10 green paper felt markers) and two boxes (or make a paper box). Place 10 red felts in one box and 10 green felts in the other. Read the following story problem.
"I went to the store yesterday and wanted to buy some green markers and some red markers. When I got to the store, the markers only came in packages of 10. I only wanted 10 markers in total because I didn’t have enough money for two boxes. I asked the person who ran the store if I could buy 10 markers, some green and some red. She said she didn't know how to do that so I told her my Grade 1 class would help me figure it out."
Remove the markers from the box and place them outside the box. Ask, "If I only want 10 markers in this box, how many green markers should I put in and how many red ones?" Have students suggest answers and place the appropriate number of markers in the box. Ask for another volunteer to come up and provide a different solution to the problem. Ask, "Is this a different solution? How do you know? Is there another possible solution?" Continue until several solutions have been presented.
Have students find a partner. Give each pair 10 green interlocking cubes and 10 red interlocking cubes. Tell them that you would like them to write down the answers you just figured out together on the sheet provided so that you can take them back to the store owner. On a large sheet, have them draw the different combinations of red and green markers that add up to 10 and write the addition sentence beneath each drawing. They can use the interlocking cubes to check that they have remembered all the combinations.
4. Story Problem
Have students write or create story problems for a given number sentence. Tell them that the number sentence you are giving them is the answer to their story problem, e.g., 9 + 6 = 15 or 11 – 3 = 8, and you would like to know a story problem that would fit the given answer. Model two or three examples for students first.
5. Number Families
Give students three numbers in a number family, which are numbers related by addition or subtraction; e.g., 2, 9, 11. Have them write an addition and a subtraction sentence for each number family.
Look For …
Do students:

notice how when one addend goes up (e.g., 5 to 6) that the other addend must go down (e.g., 9 to 8)?

recognize that 11 + 7 = 18 is a related fact to 10 + 7 = 17?
6. Fatima
Tell students that a student, Fatima, was showing her teacher some work. Fatima wrote 5 + 9 = 6 + 8 = 14. Ask students to explain how Fatima did this and if she is correct.
7. Yeung Li
Yeung Li showed his teacher his work. He wrote 10 + 7 = 17 so 11 + 7 = 18. Was his thinking correct?