Lesson 7

Subtraction Strategies Seminar

Est. Class Sessions: 2
X

Mathematical Standards

2.OA.A
Represent and solve problems involving addition and subtraction. (2.OA.A.1)
2.OA.B
Add and subtract within 20. (2.OA.B.2)
2.MD.B
Relate addition and subtraction to length. (2.MD.B.6)
2.MD.C
Work with time and money. (2.MD.C.8)

Standards for Mathematical Practice

MP2.
Reason quantitatively.
MP4.
Model with mathematics.
MP5.
Use appropriate tools strategically.
MP6.
Attend to precision.
MP8.
Look for and express regularity in repeated reasoning.

Students participate in a "strategy session" to discuss counting and reasoning strategies to solve subtraction problems within 20. They build a Subtraction Strategies Menu for the Facts and discuss which strategies seem to be better suited for different subtraction facts. Students then practice using counting and reasoning strategies to solve subtraction problems.

Content in this Lesson

  • Representing subtraction situations using multiple representations (e.g., stories, drawings, counters, number sentences, number lines, ten frames) [E1].
  • Using mental math strategies and reasoning strategies (e.g., using doubles, making ten) to solve subtraction problems within 20 [E2].
  • Using subtraction to solve one- and two-step word problems involving situations of separate/take away, part-whole, and compare [E3].
X

Materials for Students

Daily Practice and Problems Lesson Homework Assessment

Student Book

 Student Activity Book

Teacher Resources

 Teacher Guide - digital

Supplies for Student Groups

20 connecting cubes
4–5 Show Your Strategy Cards. See Materials Preparation.

Materials for the Teacher

Display of Subtraction Strategies Menu for the Facts (Student Activity Book) Page 35 or Reference
Display of Show Your Strategy Card Display Master (Teacher Guide) from Lesson 3
Display of Here's What I Thought Master (Teacher Guide) from Lesson 3
Display of Trip to Grandma's Corner Store (Student Activity Book) Pages 37–40
Prepared sets of Show Your Strategy Cards Master (Teacher Guide) from Lesson 3. See Materials Preparation.
Unit 1 Assessment Record
chart paper
connecting cubes
tape

Materials Preparation

Prepare Strategy Charts. Display and write the following titles on separate sheets of chart paper: "Counting Strategies" and "Reasoning Strategies." Leave these charts on display throughout the rest of the unit.

Prepare Show Your Strategy Cards. Make 36 copies of the Show Your Strategy Cards Master and cut them apart so you have 72 cards. Select facts from the list in Figure 1 including 12 − 9, 16 − 7, 8 − 6, 5 − 3, and 14 − 6 and record a different subtraction fact on each card. See Figure 2. The subtraction facts in each group can be solved using similar strategies. Keep the following cards separate to use for demonstration purposes at the beginning of the lesson: 12 − 9, 16 − 7, 8 − 6, 5 − 3, and 14 − 6. You will need 4–5 strategy cards from different subtraction groups for each student group in your class.

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Figure 1: Subtraction facts organized by strategy


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Figure 2: Prepared Show your Strategy Card

TIMS Tip

If you have a small class, record only some of the subtraction problems. Choose facts that lend themselves to different counting and reasoning strategies.

Assessment in this Lesson

Assessment Expectation Assessed
What Strategy Did They Use
Student Activity Book
Pages 41–42
E1.
Represent addition and subtraction situations using multiple representations (e.g., stories, drawings, counters, number sentences, number lines, diagrams, ten frames).
E2.
Use mental math strategies and reasoning strategies (e.g., using doubles, making ten) to solve addition and subtraction problems within 20.