Teaching Decomposing Numbers in Kindergarten

This post was originally published in February 2015 and was updated in November 2026.

If you’re looking at A6.5 (decompose quantities to 10) and you’re wondering how to teach it so students understand it and follow it up with practice students actually want to do, I’m here to help!

I first wrote about teaching decomposing back in 2015. My Decomposing Numbers units have had a few aesthetic updates since and last year I updated the curriculum language inside it. The actual expectation hasn’t changed though so if you’ve taught this expectation in the past, rest assured because not much has changed.

Everything in this post comes from my years in the classroom. As always, please use whatever works for you and your students. ☺️

In this post, I share:

• What the 2026 curriculum expects
• Why I teach decomposing before composing
• A nine-day progression for teaching decomposing, day by day
• Hands-on centres for continued practice
• Word problems, plus a digital option
• Possible look-fors as students decompose

What the 2026 curriculum expects

The 2026 Ontario Kindergarten math curriculum includes one expectation for decomposing:

• A6.5: decompose quantities to 10

It’s one of the expectations where the numbering changed but the actual expectation has stayed the same. In my 2026 math scope and sequence, decomposing sits in February and is followed by composing, after students have had time to work with numbers to 10 earlier in the year.

A few notes that might save you some questions:

• What does “decompose” mean? To decompose a number means to take it apart. Students show how one number can be broken into smaller parts: 6 can be 3 and 3, or 4 and 2, or 5 and 1.
• Which numbers should I start with? I started with 5 and worked up to 10, one number or pair of numbers at a time.
• Do I need to teach both sentence frames? No. You can teach “___ and ___ make ___” and “___ and ___ = ___” or also “___ = ___ and ___”, or choose just one. If introducing them all feels like a lot for your students, choose the one that works best for your class.

Why decomposing before composing?

One question I get a lot is why decomposing before composing? I teach decomposing first because it helps students understand that numbers are made of smaller parts.

For example, we start with 5 counters and explore how we can split them into groups of 3 and 2, or 4 and 1. Students can see that the parts change, but we still have 5 altogether.

Once students have explored these relationships, we build on that understanding by putting parts together to make a whole.

Decomposing lays the foundation for composing, and composing lays the foundation for addition!

My nine-day progression for teaching decomposing

Here’s the sequence I used in my lesson plans, which begins with large-group practice and moves toward word problems. Every class is different, so please stretch it, shorten it or reorder it to suit your students. (The lesson plans, mats and recording sheets for all nine days are in my printable Decomposing Numbers unit.)

Day 1: Introducing decomposing with 5

I started by introducing the learning goal and success criteria so students knew what we were working on:

• Learning goal: We are learning to decompose numbers. Decompose means to take apart.
• Success criteria: I can show how one number can be broken apart into smaller numbers.

I also introduced the sentence frames, “___ and ___ make ___” or “___ = ___ and ___”, so students had the language to talk about what they did.

For the activity, I used a five-frame Shake & Spill. I drew a large five-frame on chart paper with the title Decompose 5! and put 5 double-sided counters in a cup. Shake and spill the counters onto the carpet, arrange them by colour on the five-frame and complete the decomposing sentence together. (I used magnetic letters so we could reuse the “mat” a couple of time. Repeat as time allows.

Day 2: Decomposing 6 and 7

Review the learning goal and success criteria, then do the same Shake & Spill activity with 6 and 7 counters on a six-frame and a seven-frame.

Day 3: Decomposing 8 and 9

Same activity as yesterday, but with 8 and 9 counters on an eight-frame and a nine-frame.

Day 4: Decomposing 10

One more day of Shake & Spill, this time with 10 counters on a ten-frame.

Once students know the routine, Shake & Spill makes an easy independent centre. Print the mats on cardstock, laminate them and put them out with dry-erase markers. Students can record what they spill in the boxes and complete the decomposing sentence underneath. The printable also has a recording-sheet version, so you can introduce one number a day until every number has been practised.

Day 5: Decomposing a variety of numbers

Now that students have practised 5 through 10, it’s time to mix the numbers up with Roll & Decompose. Prepare a large die labelled 5 to 10. Students roll the die, get that many counters and decompose the number into two groups. Write the decomposing sentence on the whiteboard or chart paper, and repeat as time allows.

Students can use snap cubes, and the printable has mats and recording sheets so they can do the same activity on their own at a centre.

Day 6: Decomposing a number into 3 parts

Same activity as yesterday, but this time students break the number into three groups. Write the decomposing sentence on the whiteboard or chart paper, and repeat as time allows.

Day 7: In & Out

Show students how to play In & Out. They grab a handful of small counters and count them out, scoop the counters up and drop them into the pan. Then they talk about which counters are in the plate and which are out of the plate. They count the ones in the plate and record that number, then count the ones outside of the plate and record that number. Practise stating the decomposing sentence together, and repeat as time allows. This was one of my student’s favourite centres when I was in the classroom!

I hot-glued a small paper plate inside a reusable roasting pan, and set out small manipulatives like snap cubes. If a pan isn’t handy, the printable has a mat that works the same way, where the plate is a circle but if you can grab one from the dollar store, the pan’s sides do contain the cubes well and prevent them from flying all around the table/floor so I recommend it!

Day 8: Problem solving, day 1

We’ve built up the foundation so now we’re finally ready to introduce decomposing word problems. If you haven’t taught problem-solving strategies yet, you may want to start there before Day 8. I read a word problem aloud, then used strategy cards to model each step:

1. Understand the question. Read or listen to the problem and find the important information.
2. Make a plan. Think about what the problem is asking and decide how to solve it, with manipulatives or a drawing.
3. Try my plan. Organize manipulatives or pictures clearly to show my thinking.
4. Talk about my thinking. Use important information from the question to explain the answer and the steps taken (“The answer is…”, “First I…”, “Then I…”, “I know this because…”). Some students may also enjoy writing about it.

For the first problem, I used:

There are 8 cookies. Some are vanilla and some are chocolate. How many could be vanilla and how many could be chocolate?

The word “could” matters. There isn’t only one right answer, so students can show their thinking in more than one way, and talking about the different answers is a great part of the lesson.

Day 9: Problem solving, day 2

Try another problem the same way. In my plan, the problem is about 9 balls in three colours, blue, red and yellow.

If you’d like more problems, here are a couple of extras from my lesson plans:

• There are 7 shapes in the bag. They are circles or triangles. How many of each shape could be in the bag?
• If you have an 8-piece pizza, how could you share your pizza?

Students can colour in the pictures with dry-erase markers or use coloured counters like bingo chips, flat marbles or snap cubes to show their thinking. My printable word problems come in three versions: full-colour centre mats, centre mats with just the important colour words coloured in, and worksheet style. Choose the one that fits your class best.

Decomposing centres for continued practice

Once students know the routines from the nine days, these centres give them more time with the same idea. They use materials you likely have in your classroom already (counters, snap cubes, small manipulatives), and they’re a good example of educator-directed play: students are playing with the materials, and the skill is built in on purpose. I slowly introduce them, usually one new centre after every lesson or two. As always, choose the ones that suit your students best!

Hands-on centres

Decomposing Mats:

I used these mats with double-sided counters or coins. Print them on cardstock and laminate them for durability. Students can place the counters on the mats or draw them in with dry-erase markers. The sorting mats help students separate counters by colour so they’re easier to count.

Grab & Decompose

Students grab a handful of counters and count them. Then they separate them into two piles (or two colours) and count each pile. If your students would like more support, offer only two colours, like red and blue bears. Students record the matching decomposing sentence underneath.

Number Bracelets

Make number bracelets with beads and the printable number cards. Students move the beads to decompose each number, then record the different ways they decomposed it on the recording sheet. It’s a small, tactile activity, and it makes the idea that one number can be made in many ways easy to see.

Roll & Decompose and In & Out

Both of these whole-group activities from the progression also work well as centres, using the printable mats and recording sheets.

Recording their thinking

The I Can Decompose! recording sheets are simple sheets you can add to any decomposing centre, so students can show their thinking no matter which materials they’re using.

Word problem centres

Set out the word problem mats with coloured counters, snap cubes or dry-erase markers, and let students show how they solved each problem. Because the problems ask how many could be each colour, students can come back to the same mat and find a different answer.

Decomposing with Google Slides

If you’d like a no-prep option, I created a digital version for projecting and teaching or for use at a centre. Students decompose 5 to 10 using pictures of shapes, cubes, counting bears, jellybeans, linking chains and counters, and then drag numbers or type into the boxes to complete the sentence. There are “Make Your Own” slides where students choose their own number and break it into two or three parts, plus six problem-solving slides with apples, toast and jam, shapes in a bag, popsicles and gumballs. You can learn more about the Google Slides here.

Tips for planning and differentiating

• Start small. Spending a full day on 5 gives students time to get comfortable with the language before the numbers get bigger.
• Let materials do the supporting. Offering two colours of counters, or a frame to place them in, can make it easier to see the parts. Take them away when students are ready.
• Stretch when it makes sense. Roll & Decompose into three parts, the Make Your Own slides and larger numbers are all easy ways to extend the learning.
• Revisit it often. A quick “How many ways can we make 7?” works well at a centre or during a transition.

Possible look-fors as students decompose

These are some starting points for what you might notice as students decompose. They aren’t a checklist, since every student will show their learning in different ways.

• Shows a number in two parts using counters or other materials
• Counts each part and the whole
• Notices that the parts can change while the total stays the same
• Finds more than one way to decompose the same number
• Begins to try breaking a number into three parts
• Records the matching decomposing sentence, with support as needed
• Talks about their thinking using words like “and,” “make” and “altogether”

Free Decomposing on Rings printable

I originally made this activity with unifix cubes, but then I found these rings in the party section and thought they would work even better! Students put the rings on their fingers, decompose the number, and record how they split it, like “2 and 1 and 2 make 5.”

There are two versions: one for decomposing on one hand (shown above) and one for decomposing on two hands. You can grab both for free below.

If you’d like these lessons ready to go

I put this sequence together in two versions:

• Kindergarten Decomposing Numbers Lessons & Centres (Printable)
• Digital Math for Kindergarten | Decomposing Numbers Activities | Google Slides™

Decomposing numbers is also included in the Ontario Kindergarten Math System.

I hope these ideas help make your planning a little easier!

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