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Addition and Subtraction Within 20

A 45-minute Grade 1 lesson that replaces counting on fingers with three strategies — make ten, near doubles, and count on from the larger number.

Addition and Subtraction Within 20 is a free 45-minute Grade 1 maths lesson plan for Common Core standard 1.OA.C.6 — add and subtract within 20, quickly and accurately within 10. It is timed across 5 sections, gives the exact wording to use where the wording carries the mathematics, names 3 misconceptions with the teaching move that addresses each, and ends with an exit ticket and a printable worksheet with its answer key.

Grade:
Grade 1
Length:
45 minutes
Standard:
1.OA.C.6

Grade 1 · Operations & Algebraic Thinking

1.OA.C.6

Add and subtract within 20, demonstrating fluency for addition and subtraction within 10.

Objective

Students will be able to add and subtract within 20 using a chosen strategy, and explain why they chose it.

Students are successful when they can

  • Solves 8 + 6 by making ten, and can show the decomposition.
  • Solves 7 + 8 by relating it to the double 7 + 7.
  • Starts a count-on from the larger addend rather than the first one written.

What you need

  • Double ten frames, one per pair
  • Counters, 20 per pair
  • Strategy cards: MAKE TEN / NEAR DOUBLE / COUNT ON
  • The printable practice sheet linked at the end of this plan

The lesson

Warm-up — partners to ten

5 min
  1. Rapid-fire the make-ten partners: you say 6, class says 4.
  2. Go out of order and include 10 and 0. Sixty seconds, no writing.
  3. This is not revision for its own sake — the make-ten strategy below is unusable if these are not instant.

Teach — three strategies, one problem each

14 min
  1. Write 8 + 6. Build it on the double ten frame: eight in the first, six in the second.
  2. Move two counters across so the first frame fills. Now it reads 10 + 4. Write both equations under each other, 8 + 6 = 10 + 4 = 14.
  3. Write 7 + 8. Ask what is nearby that they already know. Draw out 7 + 7 = 14, so 7 + 8 is one more.
  4. Write 3 + 9. Ask where they would start counting. Establish that starting at 9 means three steps, starting at 3 means nine — same answer, a third of the work.
  5. Post the three strategy cards. They stay up for the rest of the unit.
“Every one of these gets the right answer. We are choosing between them on effort, not on correctness.”

Guided practice — name the strategy first

13 min
  1. Give pairs six problems: 9 + 5, 6 + 7, 2 + 8, 8 + 8, 4 + 9, 7 + 6.
  2. Rule: before solving, they must point at a strategy card. Answer second.
  3. Circulate and ask why that card. A defensible wrong choice is fine today. Not choosing is not.
  4. Bring the class back for 6 + 7 specifically — it is defensible as a near double and as a make ten, and hearing both is the point.

Independent practice

10 min
  1. Students work a mixed set alone, strategy cards still displayed.
  2. Require the strategy name written next to each answer. Answers alone do not tell you what to reteach.

Close

3 min
  1. Put 9 + 6 on the board and take a show of hands for each strategy.
  2. Ask one student from each group to justify. Do not rank them.

What goes wrong, and why

Each of these is a reasoning error rather than carelessness. The fix addresses the reasoning.

Counts on fingers from one for every problem, including 2 + 8.

Why: Counting from one is reliable and has never failed them. Until a problem is big enough that finger counting actually breaks, there is no reason to adopt anything else.

Fix: Do not ban fingers — make them insufficient. Move to sums past 20 for two problems. The strategy becomes the easier option rather than the imposed one.

Uses make-ten but loses the leftover: 8 + 6 becomes 10.

Why: The decomposition step is being treated as the whole answer. They moved two across, filled the frame, and stopped at the milestone.

Fix: Insist on writing the intermediate line 8 + 6 = 10 + 4 before the answer. The 4 has to be on paper before it can be forgotten.

Subtraction is answered by counting down one at a time, and 15 - 8 takes fifteen seconds.

Why: Subtraction has been taught as a separate operation with its own procedure, so the addition facts just built are not available to it.

Fix: Ask '8 plus what makes 15?' with the double ten frame in front of them. Once they see subtraction as a missing addend, the make-ten work transfers whole.

If they are not there yet

  • Restrict to sums within 10 and use a single ten frame until make-ten is automatic there.
  • Pre-fill one frame so only the moving-across step is left to do.
  • Give the doubles as a printed reference. Near doubles are useless without the doubles.

If they finish early

  • Give 8 + 6 and ask for two different strategies with a written justification for each.
  • Extend to three addends: 8 + 6 + 2, where noticing the 8 and 2 first is the whole game.
  • Ask which strategy they would use for 19 + 5, and whether their answer would change for 19 + 15.

Exit ticket

Solve 9 + 7. Write which strategy you used and why you picked it.

What to look for: The answer 16 with 'make ten, because 9 needs 1' is full marks. The answer 16 with no strategy named tells you nothing and should be followed up in person. A wrong answer with a correctly named strategy is a better position than a right answer with none — the reasoning is sound and only the execution needs a nudge.

Printable practice for 1.OA.C.6

Free to print and copy, answer key included. Each sheet can generate a fresh set of problems for a retake.

Questions about Addition and Subtraction Within 20

How long does the Addition and Subtraction Within 20 lesson take?

45 minutes, split across 5 timed sections: warm-up 5 min, teach 14 min, guided practice 13 min, independent practice 10 min, close 3 min. The minutes are stated per section and add up to the stated length, so the plan can be cut or extended at a section boundary rather than abandoned halfway.

Which standard does Addition and Subtraction Within 20 teach?

CCSS.MATH.CONTENT.1.OA.C.6 — 1.OA.C.6, Operations & Algebraic Thinking for Grade 1: “Add and subtract within 20, demonstrating fluency for addition and subtraction within 10.” In plain terms, add and subtract within 20, quickly and accurately within 10.

What do I need to teach this lesson?

Double ten frames, one per pair, counters, 20 per pair, strategy cards: MAKE TEN / NEAR DOUBLE / COUNT ON and the printable practice sheet linked at the end of this plan. Everything listed is either ordinary classroom equipment or a free printable from this site — there is nothing to buy and nothing to prepare beyond photocopying.

What mistakes should I expect in this lesson?

Three, each a reasoning error rather than carelessness: counts on fingers from one for every problem, including 2 + 8; uses make-ten but loses the leftover: 8 + 6 becomes 10 and subtraction is answered by counting down one at a time, and 15 - 8 takes fifteen seconds. The plan gives the thinking behind each one and the teaching move that addresses the thinking rather than the symptom.

How do I know whether the lesson worked?

The exit ticket asks: “Solve 9 + 7. Write which strategy you used and why you picked it.” The answer 16 with 'make ten, because 9 needs 1' is full marks. The answer 16 with no strategy named tells you nothing and should be followed up in person. A wrong answer with a correctly named strategy is a better position than a right answer with none — the reasoning is sound and only the execution needs a nudge. That tells you whether the class needs a reteach or a thirty-second conversation before you plan tomorrow.

Is there a worksheet to go with Addition and Subtraction Within 20?

Yes — 2 printable 1.OA.C.6 worksheets, linked at the end of the plan and free like the rest of the site. Each one comes with an answer key and 25 versions, so the practice after the lesson can be a different paper on every desk.

Is Addition and Subtraction Within 20 free to use?

Yes. The plan, its printables and their answer keys are free to read, print and photocopy for your own class, with no account and no email capture. It was last reviewed on 4 September 2026. Please do not resell it or republish it as your own.

Last reviewed 2026-09-04. Aligned to 1.OA.C.6 of the Common Core State Standards for mathematics.