CCSS.Math.Content.2.OA.B

CCSS.Math.Content.2.OA.B is a cluster heading. These are the individual standards under it.

• 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.

01

What Students Need to Do

Students find sums and differences mentally and accurately. They use strategies such as making ten, using doubles, and connecting addition facts to subtraction facts.

02

What Mastery Looks Like

Students answer addition and subtraction facts accurately and without counting every object. They use known facts, make-ten strategies, doubles, or related facts to explain their thinking.

03

Common Misconceptions

Students may treat subtraction as commutative and think 6 − 4 equals 4 − 6. They may miscount when crossing ten or confuse related facts such as 8 + 7 and 15 − 8.

04

How to Assess It

Give an exit ticket with 9 + 6, 14 − 8, and 7 + 8. Ask students to solve mentally and show one strategy for any problem.

1. 01

   Give pairs ten-frames and counters to model 8 + 7 and 15 − 8 by making or breaking apart ten.

2. 02

   Ask, “How are 7 + 8, 8 + 7, 15 − 7, and 15 − 8 connected?” Students draw and explain.

3. 03

   Play Fact Family Match with cards showing equations and matching number triangles, such as 6, 9, and 15.

4. 04

   Set up a classroom store with prices under 20 cents, then have students find totals and change using play coins.

• 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

  The 1st Grade version of this standard.

• 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 + ...