Decomposing Numbers - Why We Teach This In Kindergarten

Decomposing numbers means to break down numbers into their sub-parts. Common Core standards has kindergarten students decomposing numbers in two ways.

The first is to decompose numbers into their tens and ones (focus on numbers 11-19) and the second is to show how any number 1-10 can be created using a variety of addends.

I want to focus with you on the NBT.1 Common Core standard which addresses the tens and ones (or place value) aspect of breaking and creating numbers.

Let’s look at:

1. how it develops
2. how we can practice regularly
3. how we extend it for our advanced or accelerated kinders

Since there is so much to cover – I’ve broken it down into three parts. This is part 1 – why would we teach this standard in kindergarten and why do I even talk about it so much on this blog?

Understanding decomposing/composing numbers as teachers

Okay teachers – let’s break it down. There are two main pieces of this standard:

• The first is using objects and words to show that teen numbers have a group of ten and some ones.
• The second is expressing this break down using equations.

When I first came across this standard, I was confused and felt like I truly didn’t understand the value in teaching it. Little did I know what I’d find when teaching it daily in our calendar routine and small group math lessons.

Why do we expect them to decompose and compose numbers?

{And why do I keep writing about it?}

Let’s look long term. The simple answer is because there is value in students being able to see the groupings, relationships and patterns in numbers. We are laying the foundation for students to be able to eventually solve 53+12 and see that they can manipulate it:

50+15

or 60+5

or 50+10+3+2

or any other variety of ways to see the quantity as it makes sense to them.

Now that’s the bigger picture and carries us into older grade level Common Core standards… so lets bring it back down to our kindergarten level.

We are working on understanding that numbers 11-19 have a group of ten and then ones.

Seeing numbers broken down into a pattern of their groupings of tens and then the addition of some ones makes these numbers palatable and simple.

Learning how to compose and decompose numbers this way gives them a “visual” {especially if you are representing with ten frames} to what 6, 16 or 67 really looks like and is.

Connecting the visual and the number

The cool thing is that by teaching this foundation of how to compose and decompose numbers 11-19 (and beyond) into their groups of tens and ones – they begin to actually understand why 16 has a one and then a six.

When this clicks, they get so excited that they can’t wait to see if their new understanding applies to “bigger numbers.” And when they begin working on numbers to 99, there is some serious magic that happens.

Basically, this standard is huge!

It gives meaning to the number form and totally translates into all other math concepts. I’m not kidding. I’ve never come across a standard (other than counting 1:1) that has so much impact on other standards and is the jumping off point to see kids grow by leaps and bounds in their math skills!

Here are some lesson plans I’ve written about so you can see it in action –

• How to Teach Counting by Tens, Then Adding Ones
• A Sample Decomposing Lesson
• Why Does 10+6=16?
• Learning Decomposing with Words

but don’t forget to read the next post in this series so you can find easy ways to work on this key skill!

Continue Reading >> Part 2