CCSS.Math.Content.2.OA.B.2
The Standard
Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers.
Common Core State Standards for Mathematics · Operations and Algebraic Thinking
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students solve addition and subtraction facts to 20 quickly and accurately. They use strategies such as counting on, making ten, doubles, and related facts, then recall one-digit addition facts.
What Mastery Looks Like
- Students answer mixed facts accurately within a few seconds, without counters or drawings. They can explain a useful strategy when a fact is not recalled immediately.
Common Misconceptions
- Students may count every quantity from one instead of using known facts. They may confuse subtraction facts, reverse the numbers, or miss how addition and subtraction are related. Some memorize answers without recognizing patterns such as doubles or making ten.
How to Assess It
- Give a two-minute exit ticket: 8 + 7, 9 + 6, 13 - 5, and 16 - 9. Ask students to solve mentally and explain one strategy.
Lesson moves
Ways to Teach It
Use counters and ten-frames to build 8 + 7, then move counters to make ten and find the sum.
Ask students to explain two ways to solve 14 - 6, then compare which method feels faster and why.
Play fact-family bingo using addition and subtraction equations connected to the same three numbers.
Set up a classroom store where students mentally find totals and change for prices up to 20 cents.
Free download
Printable 2.OA.B.2 Worksheet
A ready-to-print activity worksheet aligned to CCSS.Math.Content.2.OA.B.2, with an answer key for the teacher on its own page. No account needed.
PDF, US Letter, prints cleanly in black and white.
Download the worksheetLearning progression
Where This Standard Sits
See the whole path on the Operations & Algebraic Thinking progression map.
Before This Standard
If students are struggling here, check these first.
- CCSS.Math.Content.1.OA.C.6
Grade 2 fact fluency within 20 depends on Grade 1 strategies like making ten, decomposing, and inverse relationships.
- CCSS.Math.Content.1.OA.C.5
Counting on connects number sequence to adding and subtracting, supporting later mental strategies and fact fluency within 20.
- CCSS.Math.Content.K.OA.A.5
Quick facts within 5 are needed for counting on, decomposing, and making ten when adding and subtracting within 20.
What This Unlocks
Mastery here sets students up for these next.
Keep exploring
Related Standards
- CCSS.Math.Content.2.NBT.B.5
Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
- CCSS.Math.Content.3.NBT.A.2
Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationship between addition a...
- CCSS.Math.Content.3.OA.C.7
Fluently multiply and divide within 100, using strategies such as the relationship between multiplication and division (e.g., knowing that 8 × 5 = 40, one knows...
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