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When students begin learning how to add 3-digit numbers, it’s important to give them multiple strategies to build number sense and confidence.
One helpful method is the 3-digit addition break apart strategy, also known as the partial sums strategy.
This approach supports students in understanding place value while also preparing them to regroup mentally – without needing base ten blocks.
If you’re looking for a way to move beyond manipulatives but still offer structure, this strategy is a great next step.
I’ve seen firsthand how much this method can help students, especially when paired with visuals and guided practice.
If that’s something you’re looking for, I have a resource that makes it easy to introduce and reinforce this strategy in your classroom.
Why Use the 3-Digit Addition Break Apart Strategy?
The 3-digit addition break apart strategy gives students a way to organize their thinking by separating numbers into hundreds, tens, and ones.
It helps them visualize each step of the addition process and reduces errors that come from trying to do too much in their heads.
This method aligns with standard 2.NBT.7, which encourages students to apply place value understanding and properties of operations when adding and subtracting.
If you’ve ever had students struggle with regrouping, this strategy can provide the structure they need to feel successful.
My students always seemed more confident once they had a system like this in place – and yours can, too.
And if you’re short on prep time (like most teachers!), having ready-made materials to support this strategy can save you time while keeping your students on task.
Step-by-Step Example: 3-Digit Addition Break Apart with Regrouping
Let’s walk through the problem:
This is one of the sample problems I include in my low-prep practice pages, and it’s great for modeling.
Step 1: Break Apart Each Number
Start by breaking apart each number by place value. This is just like writing them in expanded form.
349 becomes 300 + 40 + 9
473 becomes 400 + 70 + 3
I always have my students write the parts in boxes under each place value.
It keeps everything neat and easy to follow.
(If you want a printable version of this setup, you’ll love the layout in the resource I used with my students.)
Tip: Watch for common mistakes!
Students often write “3” instead of “300” or “4” instead of “40.”
These small errors can throw off the whole problem, so be sure to catch and correct them early.
Step 2: Add the Ones
9 + 3 = 12
(Have students write this underneath the ones box.)
Step 3: Add the Tens
40 + 70 = 110
Step 4: Add the Hundreds
300 + 400 = 700
Step 5: Add the Partial Sums Together
700 + 110 + 12 = 822
If students struggle with the final step, you can show them how to break it apart even further:
700 + 100 = 800
10 + 10 = 20
Then add the 2
800 + 20 + 2 = 822
Having the steps written out clearly can make all the difference.
That’s why I designed my practice pages to include structured space for each part of the strategy – so students stay focused and can follow along independently.
Teaching Tips for Success
- Emphasize writing each place value correctly (e.g., “300” not “3”).
- Use consistent visuals – boxes, arrows, number sentences – to support students’ thinking.
- Encourage students to always show their work. You’ll find it’s much easier to identify and correct mistakes this way.
- Use both “break apart” and “partial sums” to describe the strategy. This builds familiarity and helps during assessments when terminology varies.
Practice the 3-Digit Addition Break Apart Strategy with Ease
If you’re looking for a no-prep way to give your students more practice with this strategy, I’ve created a set of pages that walk them through each step – perfect for centers, guided groups, or independent work.
Each activity gives students a chance to break apart numbers, add by place value, and put it all together at the end.
You can use these pages to reinforce the routine or support students who need extra help with regrouping.
Click here to get the full set of break apart practice pages on TPT.
When your students have access to clear visuals and repeated practice, they’ll build the confidence they need to tackle 3-digit addition – even with regrouping.
Want to try this strategy with your students before committing to the full resource?
Download the free sample worksheets and see how it works in your classroom.
Need help or have questions?
If you need help or have questions, the easiest way to reach me is to DM me on Instagram @techieturtleteacher.
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