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Common Core Math1st GradeOperations & Algebraic Thinking

1.OA.6: Add and Subtract Within 20

Also written as 1.OA.C.6 and CCSS.MATH.CONTENT.1.OA.C.6 · Cluster: Add and subtract within 20.

Make an Addition WorksheetAll 21 1st Grade Math Standards

The Official Wording

Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 - 4 = 13 - 3 - 1 = 10 - 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 - 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

Common Core State Standards, Grade 1, Operations & Algebraic Thinking · Read it at the source · Checked October 14, 2026

What 1.OA.6 Means in Plain English

First graders solve any sum or difference within 20 with a strategy that beats counting all: making ten (9 + 6 is 9 + 1 + 5), getting back to ten (14 - 5 is 14 - 4 - 1), a known double, or a related addition fact.

Within 10 the target is fluency: 6 + 3 or 8 - 5 answered quickly and correctly, with no fingers needed. Above 10, strategies are fine. In 2nd grade the same push covers every fact within 20, and the sums are known from memory (2.OA.2).

1.OA.6 I Can Statements

  • I can add and subtract within 10 quickly and correctly.
  • I can make a ten to add numbers within 20.
  • I can use a fact I know to solve one I don’t.

1.OA.6 Worked Example

An addition fact and a subtraction fact, each routed through ten, the move that does most of the work in 1st grade.

Problem

Solve 9 + 6 by making a ten. Then solve 14 - 5 by getting to ten first.

Through ten, both ways
  1. 9 is one away from ten. Take 1 from the 6 to fill the ten.9 + 6 = 9 + 1 + 5
  2. Now it is a ten and 5 more.10 + 5 = 15
  3. For 14 - 5, first take away just enough to land on 10. That is 4.14 - 4 = 10
  4. 5 is 4 and 1, so one more still has to go.10 - 1 = 9
  5. Write both facts.9 + 6 = 15 and 14 - 5 = 9
Answer9 + 6 = 15 and 14 - 5 = 9

Check it: Use a related fact: 9 + 5 = 14, so 14 - 5 really is 9. And 15 - 6 = 9 takes the first sum back to where it started.

Common Mistakes with 1.OA.6

Fingers for every fact, even small ones

Still counts 5 + 3 on fingers in May

Try this: Practice facts within 10 in five-minute daily bursts with ten frames and partner flash cards until 5 + 3 is simply known.

Splitting the wrong number

9 + 6 written as 9 + 3 + 3, then stuck

Try this: Ask how many the bigger number needs to reach ten first, then split the other number to give exactly that many.

Stopping at ten

14 - 5: takes 4 to get to 10, then answers 10

Try this: Draw the 5 as 4 and 1 under the problem and tick off each part as it is taken away.

Where 1.OA.6 Fits

Comes BeforeK.OA.5Add and subtract within 5 fluently.K.OA.4Find the number that makes 10 with any number from 1 to 9.
Alongside1.OA.5Count on and count back to add and subtract.1.OA.4Solve a subtraction as a missing-addend problem.1.OA.3Use order and grouping to make sums easier.
Comes Next2.OA.2Add and subtract within 20 fluently and know one-digit sums from memory.2.NBT.5Add and subtract within 100 with place-value strategies.

Practice 1.OA.6

Addition Worksheet GeneratorFree ToolSums within 20 with an answer key. Start with the 9 + and 8 + facts, where making ten pays off fastest.Sums to 20Make tenAnswer key
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Subtraction Worksheet GeneratorFree ToolDifferences within 10 for the fluency half, timed lightly, then teen differences like 15 - 6 for getting back to ten.Within 10Within 20Answer key
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Quick Check

  1. Make a ten to solve 8 + 5.
  2. Solve 12 - 4 by getting to ten first.
  3. Ms. Lee’s class knows 7 + 7 = 14. How can that help with 7 + 8?

1.OA.6: Other Names

1.OA.61.OA.C.6CCSS.MATH.CONTENT.1.OA.C.6

Common Core State Standards © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved. Official wording from the Common Core State Standards PDFs at corestandards.org, last checked October 14, 2026. The explanation, I can statements, example, mistakes and practice on this page are EMStudio’s own, written beside the official wording. They are not part of the standard.