2.OA.2: Fluently Add and Subtract Within 20

I can fluently add and subtract within 20 using mental strategies.

What Your Child Needs to Know

This standard focuses on helping your child quickly and accurately add and subtract numbers within 20 without having to count each time. Students will learn mental math strategies that build number sense and math fluency, which is essential for more advanced math concepts.

This standard builds on previous addition and subtraction skills from 1st grade and prepares your child for multi-digit addition and subtraction in later grades. Mastering these basic facts will help your child solve problems more efficiently and confidently.

Real World Practice

Visual models and hands-on activities

Visual Models

1. Fact Family Triangles

Draw triangles with three numbers showing related addition and subtraction facts (e.g., 8, 5, 13 shows 8+5=13, 5+8=13, 13-8=5, 13-5=8).

2. Ten Frames

Use ten frames to visualize numbers and quickly recognize combinations that make 10, helping with strategies like "make a ten."

3. Number Bonds

Draw circles connected by lines showing how numbers can be broken apart and put together (e.g., 12 can be 8+4, 7+5, 6+6).

4. Double Facts Chart

Create a visual chart showing doubles (1+1, 2+2, etc.) and doubles plus one (3+4, 5+6, etc.) to help memorize these patterns.

Everyday Activities

1. Math Card Games

Play games like "Make 10" or "Make 20" where players combine cards to reach target sums, or "Difference of 5" where they find pairs with a difference of 5.

2. Mental Math Challenges

During daily activities, pose quick mental math problems: "If you have 12 crayons and give me 5, how many do you have left?" or "You have 8 stickers and I give you 7 more, how many now?"

3. Dice Addition/Subtraction

Roll two dice and practice adding or subtracting the numbers quickly. For more challenge, use three dice or create target numbers.

4. Counting Collections

Count small collections of items (buttons, coins, etc.) and practice adding or subtracting small amounts without recounting the entire collection.

Quick Checks

Strategies and quick activities

Strategies When Your Child Struggles

1. Use the "Make 10" Strategy

Teach your child to make combinations of 10 first, then add the rest. For example, 8 + 5 = 8 + 2 + 3 = 10 + 3 = 13.

2. Practice Doubles

Memorize doubles (1+1, 2+2, etc.) as these are usually easier to remember, then use "doubles plus one" for nearby facts (7+8 is 7+7+1).

3. Count On From Larger Number

For addition, start with the larger number and count on. For 5+9, start with 9 and count on 5 more.

4. Use Fact Families

Practice related facts together (6+7=13, 7+6=13, 13-7=6, 13-6=7) to strengthen understanding of the relationship between addition and subtraction.

5. Break Into Smaller Steps

Break harder facts into easier ones. For 9+6, think 9+1=10, then 10+5=15.

5-Minute Practice Activities

Activity 1: Fact Family Flash

Write three numbers that form a fact family (e.g., 7, 8, 15). Have your child quickly say all four related facts.

Activity 2: Beat the Clock

Create a set of 20 basic addition and subtraction facts. Time your child as they solve them, trying to beat their previous time.

Activity 3: Missing Number

Practice equations with missing numbers: 7 + ___ = 12 or 14 - ___ = 8.

Activity 4: Fact Triangles

Create triangular flashcards with three numbers. Cover one number and have your child determine the covered number using addition or subtraction.

Check Progress

Track improvement

By the middle of the year, your child should:

  • Know addition facts with sums to 10 fluently (without counting)
  • Know related subtraction facts within 10 fluently
  • Use strategies like "make a ten" for facts with sums 11-15
  • Demonstrate understanding of the relationship between addition and subtraction

By the end of the year, your child should:

  • Know all addition facts with sums to 20 fluently
  • Know all related subtraction facts within 20 fluently
  • Solve addition and subtraction problems mentally without counting on fingers
  • Apply mental strategies efficiently to solve problems

Mastery Signs

Your child understands this concept when they can:

  • Recall addition and subtraction facts within 20 in 3 seconds or less
  • Explain the strategies they use for solving facts
  • Apply fact knowledge to solve more complex problems
  • Identify patterns in addition and subtraction facts
  • Self-correct when they make errors

Differentiation

Support for all learning levels

Below Grade Level

Practice problems focusing on addition and subtraction facts within 10, using counting strategies and visual supports.

Download Practice Worksheet

At Grade Level

Standard practice with addition and subtraction facts within 20, focusing on mental strategies and fluency.

Download Grade Level Worksheet

Above Grade Level

Advanced practice applying addition and subtraction facts within 20 to solve multi-step problems and mental math with larger numbers.

Download Challenge Worksheet