Introduction to Decomposing Numbers


Jack is really starting to get interested in numbers and math. This lesson covers 3 of the kindergarten math standards which have to do with decomposing numbers. As I was putting together this lesson, I realized it required a level of thinking that Jack was never exposed to. He had to think algebraically and I wasn’t sure if it was going to be too tough for him and frustrate him. Luckily, he really seemed to enjoy it, especially because we turned the lesson into a search for “mystery numbers.”

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decomposing numbers 1 through 5(2)

Materials List for Decomposing Numbers

poster board
Post-it Notes
play money
Mystery Numbers 24-Page Lesson Plan

Step 1: Download the Kindergarten Decomposing Numbers Mystery Numbers Lesson Plan from our Teachers Pay Teachers store and complete the worksheets

Here is a sample worksheet page from the lesson:


Step 2: Set up the poster board just as you see in the pictures below

Decomposing numbers means you are breaking down a number to see the smaller numbers that make it up.  For example, the number 2 is made up of two 1’s.

mystery thumbnail 5

decomposing numbers 1 through 5

Step 3: Once you get the poster board set up, fill in the answers and cover them with small Post-It notes with questions marks on them

Here is a video explaining the objective of the decomposing numbers lesson.

Step 4: Begin the lesson with the student, start with number one and move very slowly, breaking down each number until the number 5

I quickly realized that I had to modify the lesson and use play money as a manipulative to help Jack understand the concept better:

He was finally getting it, this was so exciting!

Step 5: Complete the assessment from the Mystery Numbers lesson

Here is a sample page from the assessment: