Common Core Standards highlight building number sense with third graders. To build number sense, we have taught several strategies for addition and subtraction: using a hundreds chart, an open number line, and place value blocks.
This anchor chart shows how to subtract using an open number line. The hardest part for the students is using the skill of counting backwards, especially when going back over a ten-mark. We struggle with remembering friendly numbers.
Here is my anchor chart for using place value blocks to subtract when there is no need to regroup. We started with real place value blocks. Then we moved to the picture model. After a bit of modeling, my kiddos really caught on to this strategy well. When subtracting without regrouping, this method tended to be especially easy for them.
Ultimately, the boys decided on the standard algorithm for problems needing regrouping. This poem helped them remember to regroup.
A great online manipulatives resource is from the National Library of Virtual Manipulatives. They have base ten blocks for addition and subtraction. This can be used from a SMART board--my students would do the problems from the board. They also have Number Pieces. This app is free and is easy for the students to build the problems and solve them. Both work great to provide students with practice.
I hope this gives you some inspiration on how to help students master subtraction. Common Core has many twists and turns. It's important that whatever strategy students find and have success with that they are able to explain their thinking and tell is the strategy they choose is effective and efficient.