CCSS.Math.Content.2.OA.B
The standard
Add and subtract within 20.
Common Core State Standards for Mathematics
What this standard means
Students need quick, accurate strategies for adding and subtracting small numbers. They should use facts they know, make ten, count on, count back, break numbers apart, and use the link between addition and subtraction. The goal is not just getting answers, but choosing a strategy that makes sense.
Mastery looks like solving problems within 20 without counting every object from one. Students can explain how they got an answer and check it with the opposite operation. Common trouble spots are teen numbers, subtracting across 10, and mixing up what to do in word problems.
Ways to teach it
- Hands-on activity: Give pairs ten-frames and counters to build 8+7, then move counters to make ten and record the number sentence.
- Discussion or writing prompt: Ask, “Which is easier, 13-9 or 13-3-6, and why?” then have students explain with a drawing.
- Quick assessment: Show five flash cards, such as 9+6 and 14-8, and ask students to write the answer and strategy.
- Real-world connection: Use a pretend snack bag with 20 crackers, take some away, and have students find how many are left.
Plan a lesson for CCSS.Math.Content.2.OA.B
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Related standards
- CCSS.Math.Content.K.OA.A.5
Fluently add and subtract within 5.
- CCSS.Math.Content.1.OA.A.1
Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, wit...
- CCSS.Math.Content.1.OA.C
Add and subtract within 20.
- CCSS.Math.Content.1.OA.C.6
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 + ...