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Overview

Today students use the commutative property of addition and “make-a-ten” thinking to solve addition and subtraction word problems within 20. They will model, draw, and write equations with a symbol for the unknown.

Learning intentions

• Students will solve word problems using addition and subtraction within 20.
• Students will use objects and drawings to represent adding to, taking from, putting together, taking apart, and comparing situations.
• Students will explain strategies for finding an unknown number using an equation.
• Students will recognize that changing the order of addends can keep the sum the same.

Success criteria

• I can show a word problem with objects or a drawing.
• I can write an equation with a symbol (□) for the unknown.
• I can solve addition and subtraction within 20 and explain how I know.
• I can tell when two different addition statements have the same sum (like 8 + 3 and 3 + 8).

Curriculum links

• Operations and Algebraic Thinking — CCSS.MATH.CONTENT.1.OA.A.1 (word problems with addition and subtraction within 20, with unknowns in all positions)
• Operations and Algebraic Thinking — CCSS.MATH.CONTENT.1.OA.B.3 (apply properties of operations as strategies, including commutative and associative ideas)
• Operations and Algebraic Thinking — CCSS.MATH.CONTENT.1.OA.A.2 (solve word problems with three whole numbers whose sum is ≤ 20, using objects/drawings/equations)

Lesson structure (45 minutes)

1. 0–5 min · Warm-up (number talk). Teacher displays two addends on the board (e.g., 6 + 4 and 4 + 6) and asks, “Will the sum be the same or different?” Students give quick answers and one reason.

2. 5–12 min · Teach (model with manipulatives). Teacher uses base-ten blocks or counters to show 8 + 3 = 11, then reorders the counters to show 3 + 8 = 11, emphasizing the commutative property as a strategy. Students repeat the demonstration with their own counters while saying: “The sum stays the same.”

3. 12–20 min · Guided practice (addition word problem + unknown). Teacher reads a problem and writes a diagram: “Jada has 7 stickers. Her friend gives her some more. Now she has 12. How many did her friend give?” Teacher reminds: use a symbol □ for the unknown. Students model with counters, draw a quick picture, and write an equation using □ (students share one equation and solution method).

4. 20–27 min · Strategy mini-lesson (make a ten). Teacher shows a new problem: “There are 2 red marbles and 8 blue marbles. How many altogether?” Then adds a third amount: “and 5 green marbles.” Students help complete: 2 + 8 = 10, then 10 + 5 = 15. Students practice saying the steps and writing the related equation with three addends.

5. 27–38 min · Small groups (solve and explain). Teacher places three problem cards at stations; each includes a different structure (adding to, taking from, and putting together) with an unknown in a different position. Students rotate every ~3–4 minutes. At each station, students: model with counters or draw, complete the equation with □, solve within 20, and explain their strategy to a partner (sentence starter provided: “I know because…”).

6. 38–43 min · Whole-class share (commutative check). Teacher selects two student-made equations that are reverses (e.g., □ + 9 = 14 and 9 + □ = 14, or 9 + 5 = 14 and 5 + 9 = 14) and asks: “Do both equations match the story? How do we know?” Students justify using the commutative property idea.

7. 43–45 min · Exit ticket (quick assessment). Students answer one short word problem and write an equation with □, plus a one-sentence strategy explanation.

Resources

• Counters or base-ten blocks (at least 20 per student)
• Small whiteboards and markers (or paper + pencil)
• Word problem cards (3–4 sets, with unknowns in different positions)
• Student recording sheet with: “Draw it,” “Equation,” “Answer,” “How I solved it”
• Number line (optional) and a ten-frame poster
• Exit ticket slips
• Projector/board for teacher examples

Assessment

• Teacher checks during modeling and station work: Are students using drawings/objects and writing equations with □?
• Quick listen for explanations: Do students mention order doesn’t change the sum when using commutative property?
• Exit ticket: Correct solution within 20 and a correct equation with □ for the unknown.

Differentiation

• Support: Provide partially completed equation frames (e.g., □ + 7 = 12) and sentence starters (“I started with… then… I know because…”).
• Support: Offer a “choice board” of representations (counters, drawing, ten-frame) so students can pick what works.
• Extension: For the station that uses commutative property, ask students to write two addition equations that match the same situation (e.g., 8 + 3 = □ and 3 + 8 = □).
• EAL/SEN: Use visuals (picture on each card) and allow pointing to the counters as part of explanation; keep language prompts consistent across stations.

Exit ticket sample (for 2 minutes)

• “There were 6 birds on a tree. Then 9 more birds came. How many birds are there now?” Students draw/model, write an equation with □ (e.g., 6 + 9 = □), and answer.