Subtraction Strategies Seminar

Guess My Strategy. This game is similar to the strategy game in Lesson 3, but students guess subtraction strategies instead of addition strategies. The activity allows students to practice using subtraction strategies before you assign the assessment.

Write the problem 11 − 3 on a display. Ask the class to watch carefully but not to say anything as you solve the problem. Remind students that there are several different strategies that someone can use to solve the problem. Their job is not to solve the problem, but instead to watch you and guess your strategy so they can describe it.

Use a number line to demonstrate your strategy. Without explaining what you are demonstrating, start at 11 and make 3 jumps back to 8. Write "8" as your answer to the problem. Ask students to identify and explain your subtraction strategy. If they describe it but don't name it, call it the "counting back" strategy. Write the steps on the display. See Figure 8.

Then do a silent demonstration of the using ten strategy. Write the same problem, 11 − 3, on a display. Use ten frames to demonstrate the problem. Place 10 connecting cubes or counters in one ten frame and take away 3. Write, "10 − 3 = 7." Add one more counter and write, "11 − 3 = 8."

Ask volunteers to explain your strategy. Write the steps on the board and ask students to justify them, as shown in Figure 9. Accept descriptions that reasonably fit the steps you modeled while solving the problem. Encourage students to break it down into both mental and action steps.

Assign the What Strategy Did They Use pages in the Student Activity Book to assess students' understanding of subtraction strategies. Have connecting cubes readily available.