I have struggled to find a good breakdown for decomposing numbers. I wanted to start with breaking down numbers before I started subtracting. Most of the time students know how to subtract only by using the algorithm. They can "carry a one" or "change it to a ten" , but they have NO CLUE as to why they are doing it or what it really looks like.
This sheet is a good walkthrough/talkthrough activity.
It starts with what they know about place value and representing numbers. Then it looks at what decomposing really is and how we use it when we subtract.
You can use this as an introduction, review, small group activity, etc.
I pull it up on my smart board and give partners and small groups a copy. They can walk through it with me. I have them show it with the base ten blocks as we do it together.
I am including another page (front and back) of a chart. I start them with examples of breaking down and decomposing. Then I have a blank chart where they can practice as well. This reviews many areas of place value and really ties to the NBT2 standard of USING place value to subtract. I want to build a good foundation for my students.
Decomposing is often hard for us teachers as well since we were taught the "short cut" algorithm way. This is a good breakdown for any teacher wanting some help teaching what decomposing really looks like! :)