K.OA.3: Decomposing Numbers

1. Part-Part-Whole Mats

Use a diagram with a large circle (the whole) and two smaller circles (the parts). Place counters in the whole circle, then separate them into the part circles in different ways.

2. Number Bonds

Draw circles connected by lines to show how a number (the whole) can be broken into parts. For example, 7 can be broken into 5 and 2, or 4 and 3, etc.

3. Ten Frames

Use ten frames with two different colored counters to show different ways to make a number. For example, 6 can be 5 red counters and 1 blue counter, or 4 red and 2 blue, etc.

4. Domino Decomposition

Use dominoes to show how numbers can be broken into two parts (the dots on each side of the domino).

1. Sorting Games

Collect a specific number of objects (like 8 toy cars) and sort them in different ways (e.g., 5 red cars and 3 blue cars, or 4 big cars and 4 small cars).

2. Snack Sorting

Give your child a small handful of snacks (like 10 crackers or cereal pieces) and ask them to separate them into two groups in different ways.

3. Finger Play

Show a number with your fingers (like 7) and ask your child to show the same total using a different combination of fingers on their two hands.

4. Number Books

Read books that focus on breaking numbers apart. Create your own simple books showing different ways to make each number from 5 to 10.

5. Number Puzzles

Create simple puzzles where children match two parts to make a whole number.

1. Start with Manipulatives

If your child struggles with abstract concepts, use physical objects they can separate into groups.

2. Use a Systematic Approach

Start with all counters in one group, then move one at a time to the other group to find all combinations.

3. Record Findings

Help your child record each decomposition they find (e.g., 7 = 5 + 2, 7 = 4 + 3, etc.).

4. Connect to Stories

Create simple stories about breaking numbers apart. "You have 8 toys. Some are on the shelf and some are in the toy box. How many could be in each place?"

5. Focus on Patterns

Help your child notice patterns in decompositions. For example, as one part increases by 1, the other part decreases by 1.

Activity 1: Ways to Make a Number

Choose a number between 5 and 10. Use counters or drawings to find all the ways to break that number into two parts.

Activity 2: Shake and Spill

Put counters of two different colors in a cup (totaling a number like 6 or 8). Shake and spill them. Count how many of each color to see one way to decompose the number.

Activity 3: Number Bracelets

String beads of two different colors to show different ways to make a number. For example, 7 beads could be 3 red and 4 blue, or 5 red and 2 blue, etc.

Activity 4: Missing Part

Show a certain number of objects, then hide some. "I have 9 counters. You can see 6. How many am I hiding?"

By the middle of the year, your child should:

• Decompose numbers up to 5 in more than one way
• Use objects or drawings to show different decompositions
• Begin to record decompositions with adult support

By the end of the year, your child should:

• Decompose numbers up to 10 in multiple ways
• Record decompositions using drawings or equations
• Find a missing part when given a whole and one part
• Recognize that there are multiple ways to break apart a number

Simple Assessment:

Ask your child to show you all the ways to make 7 using counters or drawings.
Give your child 9 objects and ask them to separate them into two groups in different ways.
Show 8 counters with 5 visible and 3 hidden. Ask how many are hidden.