Base ten blocks are a great way to help students see what’s happening when they add 2-digit numbers.
I’ve put together the resources and support below to help you teach the strategy, give students practice, and address common mistakes.
Base ten blocks can help students make sense of 2-digit addition because they can actually see the tens and ones they are adding. A few simple teaching moves can make the strategy even more effective.
Start without regrouping.
Give students some problems where the ones add up to 9 or less before introducing regrouping. This gives them a chance to get comfortable representing tens and ones and combining the numbers.
Have students identify the tens and ones first.
Before they start adding, ask students to look at each number and tell you how many tens and how many ones it has. This helps them focus on place value instead of just treating the numbers as two digits.
Ask questions instead of just having students count.
Try asking, “How many tens do you have?” or “What does this ten represent?” This encourages students to connect the blocks to the numbers they are working with.
Make regrouping about the math, not a rule to memorize.
When students have 10 or more ones, have them physically trade 10 ones for 1 ten. Talk about what changed and what stayed the same. The goal is for students to understand that they aren’t getting rid of 10. They are exchanging it for another way to represent the same amount.
Connect the blocks to the written work.
Once students can model the problem, connect what they see to the numbers they write. Point out how the tens and ones in their model match the tens and ones in the written addition problem. This helps students understand why the written steps work instead of simply memorizing a procedure.
Base ten blocks make it easier to spot what students understand about place value and what they are still working on. Here are a few mistakes you may see when students use base ten blocks to solve 2-digit addition problems.
What you might see:
A student combines all of the ones and writes 13 in the ones place instead of trading 10 ones for 1 ten.
What’s happening:
The student may understand that they need to add the ones, but they don’t yet understand that 10 ones can be regrouped as 1 ten.
What can you do?
Have the student physically count out 10 ones and trade them for a ten. Then ask, “Do we still have the same amount?” This helps students see that regrouping changes how the amount is represented, not how much they have.
What you might see:
The student correctly trades 10 ones for 1 ten but forgets to include that new ten when adding the tens.
What’s happening:
The student understands the exchange but is having trouble connecting the model to the next step of the addition process.
What can you do?
Have the student separate the original tens from the new ten they made. Ask, “How many tens do we have now?” Then have them recount all of the tens before writing the answer.
What you might see:
A student counts all of the blocks together without keeping track of which blocks represent tens and which represent ones.
What’s happening:
The student may be able to find the total but isn’t yet using the base ten blocks to understand place value.
What can you do?
Have the student organize the blocks into two groups: tens and ones. Ask, “How many tens?” and “How many ones?” before they begin combining the amounts. This keeps the focus on place value as they solve.
If you don’t want to make your own worksheets, I have a few resources that go along with this strategy.
If you’re teaching 2-digit addition and want all of the pieces ready to go, I’m putting together a 2-Digit Addition Toolkit that brings the strategies, practice, error analysis, and teacher support together in one place.
I’m still putting the finishing touches on it, but you can join the waitlist and I’ll let you know when it’s ready.
The Toolkit will include:
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Want to be the first to know when it’s ready?
