CCSS.Math.Content.1.OA.C.6
The standard
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 for Mathematics · Operations and Algebraic Thinking
What this standard means
Students need to solve addition and subtraction facts within 20, not by guessing or counting every object from one each time. They should use workable strategies like counting on, making ten, breaking apart numbers, using doubles, and using related facts.
Mastery looks like quick, accurate work within 10 and flexible strategy use within 20. Students should explain how they know, with numbers, fingers, ten-frames, or drawings. Common sticking points are counting backward, crossing ten, and seeing subtraction as connected to addition.
Ways to teach it
- Hands-on activity: Give students ten-frames and counters to build 8 + 6 by filling ten first, then writing the matching equation.
- Prompt: Ask, “Which is easier, 7 + 8 or 7 + 7 + 1, and why?” then have students explain with a drawing.
- Quick assessment: Show five facts, including 9 + 5 and 14 - 6, and ask students to solve and name the strategy used.
- Real-world connection: Use a snack count, “We have 13 crackers and eat 5, how many are left?” and model breaking 5 into 3 and 2.
Plan a lesson for CCSS.Math.Content.1.OA.C.6
Generate a complete lesson plan aligned to this standard, with objectives, activities, and materials. Free, no account needed.
Related standards
- CCSS.Math.Content.1.NBT.C.4
Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawing...
- 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.2.NBT.B.7
Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between a...
- CCSS.Math.Content.2.OA.B.2
Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers.