CCSS.Math.Content.1.OA.C
The standard
Add and subtract within 20.
Common Core State Standards for Mathematics
What this standard means
Students need to solve addition and subtraction problems with totals and starting numbers up to 20. They should use objects, drawings, number lines, ten-frames, and known facts. They also need to explain how they solved, not just give an answer.
Mastery looks like choosing an efficient strategy, such as making ten, counting on, using doubles, or using a related fact. Students often get stuck counting all every time, mixing up addition and subtraction, or losing track when numbers cross 10.
Ways to teach it
- Give pairs 20 counters and ten-frames, then ask them to build and record four facts such as 8 plus 7 and 15 minus 6.
- Ask, “How could making 10 help solve 9 plus 6?” and have students draw or write their strategy.
- Show five flash cards with problems within 20, and have students write the answer plus one strategy word, like doubles or count back.
- Use classroom supplies, such as 14 crayons with 5 missing, and ask students to figure out how many are left or needed.
Plan a lesson for CCSS.Math.Content.1.OA.C
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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.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 + ...
- CCSS.Math.Content.2.OA.B
Add and subtract within 20.