Two Activities to Teach Decomposing

This blog post is about teaching primary learners how to decompose numbers in more than 1 way using hands-on activities.

What is decomposing?

Decomposing is an important mathematical concept because it helps students develop an understanding of how addition and subtraction works. Students can put together (compose) or take apart (decompose) objects to represent addition and subtraction.

How to Teach Decomposing

How to decompose numbers using hands-on activities

To teach students how to decompose, you should provide them with a variety of opportunities with concrete objects. Here’s how I usually teach it.

Objects – Drawings – Writing Addition and Subtraction Expressions and Equations

Objects I use: I use 2 colored counters, linking cubes or unfix cubes, and a ten frame. You can use almost any object to teach students how to decompose!

Always Teach Vocabulary First!

For students to be successful in ALL grades in math, students need to be able to use academic language. Academic language allows students to express their understanding of how they solved a mathematical problem as well as share their thinking with others.

To teach addition and subtraction academic language, I have students sort these visual vocabulary cards with me. Students can figure out what is “put together” and “take apart” by looking at the pictures. We also briefly discuss what these terms look like by practicing putting cubes together (composing) and taking them apart (decomposing).

FREE vocabulary cards for decomposing numbers

Also, before introducing addition and subtraction symbols, make sure that you provide your students with numerous experiences with joining and taking apart objects and explaining how they decomposed a number with their partner and to you.

Additional Resources

Hands-on activities for teaching students how to decompose numbers

Remember to model how to decompose numbers and how to use academic language to explain your thinking.

Teach students to say, “1 and 4 are the same as 4” or “1 and 4 is the same amount as 5” or “1 and 4 objects is the same amount as 5 objects.”

Remember it is just as important for students to be able to explain what they are doing as it is for them to get the correct answer!

Here are 2 activities that you can play with your students that teach them how to decompose numbers.

Activity #1 Shake and Spill

What you need: You need 2 colored counters, crayons, and these recording sheets.

Students pick a number. Then, they put that many counters in a cup. They gently shake the cup and the counters will spill on the table. They count how many red and how many yellow. Next, they use their crayons to show how many red and how many yellow.

For students that are working on writing expressions, they write the sentence. For students that are working on writing equations, they can write an equation.

There are additional recording sheets for students to write an equation with the equal sign first.

Some students are not ready to write equations on their own yet and that’s okay! For the students that are not ready yet, I have them write a number sentence using “and” and “is” and for the students that are ready to write an equation, I let them. Let them explain how they decompose a number orally too.

For students that still need support with keeping track of how many they have counted, allow students to use a ten frame to help them.

Activity #2 – Build it and Break it!

What you need: You need counting cubes, crayons, and these recording sheets.

Students pick a number. Then, they grab that many cubes and build a tower by snapping them together. Next, they break the cubes. They count how many cubes are in their left hand and how many cubes are in their right hand. Last, they draw a picture recording how they broke the cubes into 2 parts. They put the cubes back together and break the cubes a different way. Last, they record the equation.

That’s it! I love the games Build It and Break It and Shake and Spill! These are fun games that you can put in your math centers for hands-on decomposing learning!