Kindergarten · Operations & Algebraic Thinking
K.OA.A.3: Decompose numbers less than or equal to 10
K.OA.A.3 is a kindergarten Common Core math standard in Operations & Algebraic Thinking. Here’s what it really covers, and how you can help your students learn it.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
The standard
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).
In plain words
Decompose numbers less than or equal to 10.
Sample questions from student practice
These questions from Bobby's Math Club are the kinds of questions your students will see. You can try answering them to see what a student might see.
Question 1 of 3
There are 5 ladybugs in total. Some are on a leaf and the rest are on a flower. If 2 ladybugs are on the leaf, how many ladybugs are on the flower?
- 2
- 3
- 4
Where students can get stuck
- Finding one way to split a number, such as 5 = 4 + 1, and believing it is the only answer.
- Thinking 6 = 4 + 2 is wrong because they expect the answer to come after the equal sign.
- Losing or adding an object while splitting 8, ending with 5 and 4, and not checking the parts still make 8.
Effective teaching strategies
- Split a group of 5 large blocks into two parts in different ways, such as 4 and 1, then 3 and 2, and ask students to find a split no one has shown.
- Write each split two ways, such as 6 = 4 + 2 and 4 + 2 = 6, so students see that the equal sign can sit on either side of the sum.
- Have students recount both parts together after splitting 8 into 5 and 3, so they check that nothing was lost or added and the whole is still 8.
Units that teach this standard
Find where K.OA.A.3 lands in the program you teach. Each unit has a guide written for families. Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence.
Bridges in Mathematics
enVision Mathematics
Everyday Mathematics
i-Ready Classroom Mathematics
Illustrative Mathematics
Math Expressions
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Families can read Splitting numbers up to 10 into two parts for a plain-language look at this skill, with three questions to try together and ideas for helping at home.
Help every student practice problem solving at home
In Bobby's Math Club, students practice at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free for every family.
See how it works for teachers
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.