If your experience has been anything like mine, you’ve likely met the student who can add within 10 but wobbles when a problem bumps into the teens. They count all, lose track, and start again. Addition within 20 can feel like a big step, because it is!
And it is an important step because addition within 20 asks children to think beyond counting to ten and begin working with tens and ones. That shift powers mental math, frees up working memory for multi-step problems, and lays the foundation for addition within 100 and beyond.
So which strategies for addition within 20 actually make a difference? And how do we build real fluency without turning it into drill after drill? Let’s talk through it, and along the way I’ll share my go-to resources and activities so you’ve got what you need to hit the ground running.
The Path to Addition Within 20
Addition within 20 doesn’t happen in isolation. It’s part of a progression that starts as early as kindergarten. All that work with five-frames and ten-frames? Helping students see teen numbers as “ten and some ones”? That’s setting them up to bridge through ten when they’re ready. The language you use now like, “How far from ten?” and “What do we need to make ten?” plants seeds for strategies they’ll use later. (If you want a teacher-facing refresher on how I make ten visible early on, I unpack it in my Ways to Make Ten post.)
In first grade, students add and subtract within 20 and aim for fluency within 10. By second grade, the expectation shifts to fluency within 20 using mental strategies, with students knowing sums of two single-digit numbers from memory by the end of the year.
Here’s something that’s really important to remember: fluency doesn’t mean rote memorization. At this stage, fluency means students can solve accurately, efficiently, and flexibly—often mentally—by using relationships between numbers (tens, doubles, and friendly numbers). Memory grows from meaning!!
When it clicks, you’ll hear strategic counting on, make-a-ten talk, doubles and near doubles, and quick use of known facts. You’ll see students choosing strategies that fit the numbers instead of using the same approach every time.
And here’s why this all matters for third grade and beyond: those same strategies scale up. Students use the same thinking to add larger numbers, adjust to friendlier benchmarks, and use that understanding to make sense of formal algorithms.
Foundational Strategies for Addition Within 20
The jump from addition within 10 to addition within 20 presents some predictable challenges:
- Counting-all habits linger; holding the first addend and truly counting on is still developing.
- Teens are tricky; place value is still consolidating, so 13 can feel like “one and three.”
- Ten isn’t seen as a helpful “bridge” yet, which can make some problems feel cumbersome.
So let’s zoom into the classroom moves that support students as they move from counting-all to flexible addition within 20.
Counting On
Counting on is often students’ first efficient shift away from counting all. Instead of starting at one and counting every object, students hold the first addend (ideally the larger number) and count up by the smaller amount. For 9 + 4, a student might say “9… 10, 11, 12, 13.” I make time for students to compare solutions so they discover why starting with the larger addend is more efficient.
Making Ten
If there’s one strategy that transforms addition within 20, it’s making ten. This approach leverages students’ growing understanding of 10 as a benchmark and their grasp of combinations that make 10. To give students meaningful practice, I use make a ten to add activities as they work towards internalizing the concept.
For a problem like 8 + 6, a student might think, “8 needs 2 to make 10. I can break 6 into 2 and 5 to get 8 + 2 + 4. So 8 + 2 = 10, and 10 + 4 = 14.”
There’s so much important thinking packed in: decomposing and recomposing, using ten as an anchor, and seeing teens as “ten and some ones.” This same break-apart thinking scales later (38 + 7 → 38 + 2 + 5) and is the backbone of the Decomposition Strategy.
Doubles and Near Doubles
Once students feel the power of ten, doubles become a steady anchor. Kids connect to the certainty of 6+6 or 8+8, and that lets them stretch to the “almost” cases. When a student says, “I know 7+7 is 14, so 7+8 is 15,” they’re using near doubles without any prompting. I lean into that language in number talks and partner shares so the +1/–1 adjustment becomes second nature. This is early compensation thinking that students can rely on as numbers get bigger.
Using Known Facts & Number Relationships
As fact knowledge grows, students start to leverage it. They don’t solve 9+6 from scratch—they notice that nine is one away from ten and think, “10+5.” The same thing happens with doubles: “If I know 5+5, then 6+5 is just one more.”
Students can also use known facts to create turn-around facts (also the commutative property of addition). For example, if students know 5 + 3 = 8, they also know 3 + 5 = 8.
To make those relationships concrete and discussable, I keep the structure visible with manipulatives and quick representations (double ten-frames, connecting cubes, open number lines, etc.) so students can model their thinking and explain why it works.
Addition Within 20 and the Place Value Connection
Tens and ones are the quiet engine behind all of this. When teens are really understood as “a ten and some ones,” making ten starts feeling like a natural next step. In lessons and centers I encourage students to use the representation that makes the most sense to them and best matches the thinking they want to show.
When I want the structure to stay front and center during centers, I pull out tens and ones activities that keep the “ten-ness” visible while students reason.
Looking Beyond Addition Within 20
As students grow in fluency, these ideas deepen and broaden. They use the same make-ten and doubles reasoning to decompose (38 + 7 → 38 + 2 + 5), to adjust to benchmarks (298 + 17 → 300 + 15), and, later, to write methods that reflect place value. Same sense-making, wider reach.
Addition Within 20 Activities that Build Fluency
Now let’s put these strategies to work. My goal is predictable routines that spotlight strategy, not speed. Here are three I return to all year, and they are all easy to dial up or down.
Ten-Frame Bridges
Students model sums like 9+4 on double ten-frames and physically move counters to complete a ten before finishing the sum. When I want this to stay fresh, I pull from my make a ten games for hands-on “making ten” centers that keep the why front and center.
Spin, Add, & Cover
The idea is simple: two spins, add them, cover the sum on a 0–20 board. Add in some intentional prompts like, “Where would a bridge to ten help here?” or “Is this a near double?” and you’ve got a winning combination.
I’ll swap boards to highlight targets around ten so the strategy choice isn’t accidental. And for year-round variety, I rotate in addition within 20 games which provide low-prep math center games that spiral make-ten and near doubles.
Build-Then-Replace
Students build a teen (say, 13 as a ten and three ones), add a few more, and “trade up” to a new ten when they cross it. This makes the bridge tangible and sets students up for regrouping later.
From Practice to Mastery of Addition Within 20
We’ve named the top addition within 20 strategies and tried them in centers; now it’s about those day-to-day moves we make that help them stick. Here are a few pointers to keep in your back pocket:
- Use concrete, representational, and abstract models, but not as a one-way staircase. As I have said before, “The magic of mathematical representations is not when they are created in isolation, but when we make connections BETWEEN them!”
- Centers do the stamina work. A small rotation of reliable routines means less time teaching new directions and more time listening to how students are thinking.
- For quick checks, I love prompts like, “Which strategy did you use and why?” or short number talks where we collect multiple ways to see the same sum. Those brief conversations tell me what to nudge next.
Remember, this is a progression. The same make-ten and doubles thinking you nurture here stretches to larger numbers, friendlier benchmarks, and written methods in later grades. Stay with sense-making, honor the representations that clarify the idea for your learners, and let fluency grow out of understanding.
