K.OA.3: Decompose Numbers Up to 10
Also written as K.OA.A.3 and CCSS.MATH.CONTENT.K.OA.A.3 · Cluster: Understand addition as putting together and adding to, and understand subtraction as taking apart and taking from.
The Official Wording
Decompose numbers less than or equal to 10 into pairs in more than one way, e.g., by using objects or drawings, and record each decomposition by a drawing or equation (e.g., 5 = 2 + 3 and 5 = 4 + 1).
Common Core State Standards, Kindergarten, Operations & Algebraic Thinking · Read it at the source · Checked October 14, 2026
What K.OA.3 Means in Plain English
Kindergartners split 6 counters into two piles in every way: 1 and 5, 2 and 4, 3 and 3, 4 and 2, 5 and 1. Each split is recorded as a drawing or an equation with the total first, 6 = 2 + 4, so the whole stays in view.
Knowing the parts inside a number is what makes later arithmetic mental instead of counted. Partners of 10 are singled out in K.OA.4, and in 1st grade these pairs become fact strategies, like solving 13 - 4 by taking 3 and then 1 (1.OA.6).
K.OA.3 I Can Statements
- I can break a number up to 10 into two parts.
- I can find more than one way to split the same number.
- I can record each split as a drawing or an equation.
K.OA.3 Worked Example
Six counters split five ways, each one recorded with the total on the left, which is the notation the standard models.
Take 6 counters. Split them into two groups in as many ways as you can, and record each way.
- Put 1 counter on the left and the rest on the right. Count the right side.6 = 1 + 5
- Slide one counter across. The left grows by one and the right shrinks by one.6 = 2 + 4
- Slide another. Now the two sides match.6 = 3 + 3
- Keep sliding. These are the earlier pairs turned around.6 = 4 + 2, 6 = 5 + 1
- Read the list. Every line still has six counters in it.1 + 5, 2 + 4, 3 + 3, 4 + 2, 5 + 1
Check it: Add the two parts in any line and count the counters again. Both come to 6 every time.
Common Mistakes with K.OA.3
Finding one way and stopping
6 = 3 + 3 written once, and the child says they are done
Try this: Slide one counter from the right pile to the left and ask what the new pair is, until the right pile is empty.
Parts that do not make the total
6 = 2 + 3, with one counter left on the table unrecorded
Try this: Have the child count both piles together out loud after every split, before anything gets written down.
Reading 6 = 2 + 4 as a mistake
“You wrote it backwards!” because the total is on the left
Try this: Read the equal sign as “is the same as” every time: six is the same as two and four.
Where K.OA.3 Fits
Practice K.OA.3
Quick Check
- Show two different ways to break 5 into two parts.
- Finish the equation: 7 = 3 + ?
- Rosa has 8 grapes to put on two plates. Name two ways she could do it.