The open number line helps students visualize 2-digit addition by using jumps to break numbers apart and add in manageable steps.
I’ve put together the resources and support below to help you teach the strategy, give students practice, and address common mistakes.
The open number line can help students make sense of 2-digit addition because they can visualize the numbers they are adding as jumps along a number line. A few simple teaching moves can make the strategy even more effective.
Start with numbers that don’t require regrouping.
Give students problems where they can make straightforward jumps of tens and ones without needing to make a new ten. This gives them a chance to get comfortable using the number line before adding the extra thinking that comes with regrouping.
Have students think about their jumps before they start.
Before students begin, ask them how they could break apart the number they are adding. For example, they might decide to jump 30 and then 4. This helps students see that the jumps represent the parts of the number they are adding.
Encourage flexible jumps.
Show students that there isn’t just one way to solve a problem on an open number line. They might add the tens first, add the ones first, or make a different combination of jumps. Asking, “What would be an easy jump to make next?” encourages students to think strategically about the numbers.
Make regrouping about the math, not a rule to memorize.
When students need to add enough ones to cross a new ten, help them notice what is happening on the number line. Ask questions like, “What ten did you land on?” or “How many more do you need to get to the next ten?” This helps students understand regrouping as a change in how they move along the number line rather than simply following a procedure.
Connect the jumps to the written work.
Once students can solve a problem on an open number line, connect each jump to the numbers in their written work. Point out how the amounts they added match the jumps they made. This helps students understand why the strategy works instead of simply drawing arrows and hoping for the best.
The open number line can make it easier to see what students understand about addition and place value and where they may need more support. Here are a few mistakes you may see when students use an open number line to solve 2-digit addition problems.
What you might see:
A student starts with 34 and draws a jump of 20 but labels it 30, or makes a jump without recording how much they added.
What’s happening:
The student may understand that they need to move forward on the number line but isn’t yet connecting the size of each jump to the amount being added.
What can you do?
Have the student say the amount of each jump before drawing it. Ask, “How much are you adding?” and “Where will you land after that jump?” This helps students connect the movement on the number line to the numbers in the problem.
What you might see:
A student makes several jumps but starts the next jump from the wrong number or gives an answer that doesn’t match where they landed.
What’s happening:
The student may understand how to make jumps but is having trouble keeping track of the numbers as they move along the number line.
What can you do?
Have students label the number they land on after each jump. Encourage them to pause and say the new number before making the next jump. This gives them a clear starting point for each step.
What you might see:
A student makes a jump that goes from 47 to 53 but doesn’t recognize that they crossed from the 40s into the 50s.
What’s happening:
The student may be able to count forward but isn’t yet using the structure of the number line to recognize a new ten and adjust their thinking.
What can you do?
Ask, “What ten did you pass?” or “How many more did you need to get to 50?” Have students break the jump into smaller parts when helpful, such as jumping to the next ten and then continuing. This helps students see how regrouping can make the addition easier to manage.
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?
