Decomposition with LEGOs

Decomposition with LEGOs

Once your child learns how to count to 10, it’s time for decomposition. Decomposition is a fancy word that means breaking down the numbers into their subparts.

Eventually, when kids can count to 100, they will be decomposing numbers into tens and ones. But for now, they only need to understand that numbers can be created using a variety of addends.  

For example, 1+4, 2+3, and 5+0 all equal 5.  

Once your child learns how to count to 10, it’s time for decomposition. Decomposition is a fancy word that means breaking down the numbers into their subparts. Eventually, when kids can count to 100, they will be decomposing numbers into tens and ones. But for now they only need to understand that numbers can be created using a variety of addends. 2+5, 3+4, and 6+1 all equal 7. In this lesson, children will practice simple decomposition with LEGOs.

In this lesson, children need to find all the different ways to make number 5, so that they can have 5 candles on their cake. It’s a very simple decomposition practice that is made fun with LEGO. Read more about First Math Lessons here.  If you are ready to move on to decomposing number 10, go here.  

Birthday Cake with LEGO candles

What you need

  • LEGO pieces: 5 red and 5 blue
  • Playdough or mud (we used a homemade playdough recipe and sprinkles)

  Decomposition with LEGOs // early math

What to do

Make a playdough cake (or a mud cake). Say, “Today is your birthday! You are decorating your birthday cake. Each LEGO piece is one candle. There is more than one way to put five candles on your cake. You can use a combination of two colors or just one color. What are you going to use?” 

If a child needs some prompting to get going, you can add, “Do you think one red and four blue will make five?” Give them some time to think about it and perhaps offer another example, “How about two red and three blue?”

Write down each answer. If a child is resistant to the idea of writing down the numbers, parents can do it for them. (I always try to make sure that my children walk away from our lessons with a pleasant feeling. Whatever they didn’t learn today, they can learn another day. My goal is to help them stay eager about learning and retain what they learn.  

Decomposition with LEGOs - writing practicePrompts


How many different ways to make 5 can you find?
Do you think you found all the possible combinations?
Do you think it’s interesting that there are so many ways to make number 5?  

If you are looking for more first math lessons.  Check out our Active Math Game and fun Counting Books and book-based Activities

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5 Responses

  1. Oh fingers are great mathematical tools!

  2. Great post!! I have 4.5 years old girl and we do decomposition using fingers, but lego is a great idea.

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