Grade 2 · Curriculum
How we teach regrouping in Grade 2
Regrouping is the hinge of second-grade math: the moment a number stops being a row of digits and becomes tens and ones you can actually trade.
Most second graders can add. What stops them in Grade 2 is what happens when a column runs past nine. That single event — carrying a ten into the next column, or borrowing one back — is where arithmetic turns into a structure instead of a set of facts. If a kid learns the procedure without the structure, they can pass a page of problems and still not be able to tell you whether 63 + 29 should land near 80 or near 100.
Grade 2 in Math Buddies extends place value to 1,000 and builds addition and subtraction fluency inside that. Regrouping is not a lesson near the end; it is threaded through two units, then revisited inside the unit that pushes past 100.
The order we teach it in
Nothing in the sequence asks a kid to regroup before they have done the same work without regrouping. Adding tens comes before adding tens and ones, which comes before adding two two-digit numbers, which comes before the trade.
| Stop | What the learner does |
|---|---|
| Add Tens | 40 + 30 as four tens and three tens. |
| Add Ones to a 2-Digit Number | 42 + 6 without crossing a ten. |
| Add 2-Digit Numbers | Columns line up; still no carry. |
| Adding with Base-Ten Regrouping | The trade: ten ones become one ten, and the learner performs it. |
| Bigger Sums with a Model | The same trade at a size where counting on stops working. |
| 10 More | One ten moves, nothing else changes. |
| Adding Stories | The trade inside a sentence instead of a column. |
| Adding Model Check | The unit's closing checkpoint, back on the model. |
Subtraction runs the mirror image in its own unit, and then the two meet:
| Stop | What the learner does |
|---|---|
| Subtract Tens | 70 − 30 as seven tens minus three tens. |
| Subtract 2-Digit Numbers | 58 − 22 without breaking a ten. |
| Subtracting with Base-Ten Regrouping | Break a ten on purpose, because the ones column is short. |
| 10 Less | Then Think Addition: 54 − 27 asked as "27 plus what makes 54?" |
| How Many More? | Comparison language — the same structure, different question. |
| Subtracting Model Check | The unit's checkpoint, back on the model again. |
The unit called Within 1000 is where it becomes automatic: hundreds added and subtracted, then a mixed Regrouping Challenge, then three-digit story problems and a final check. By the end, a learner is expected to add and subtract within 1,000 using models or drawings as needed — which is exactly how the Grade 2 standard is written.
Model first, procedure second
The lessons that teach the trade are built on a base-ten model, and they deliberately force it. A question in those lessons is not generated to be easy; it is generated so that the ones column overflows. The learner moves blocks, breaks a ten, and the number changes under their hands.
That is a deliberate teaching order. A drawing of the trade and the written method are two representations of the same idea, and the idea has to exist first. A kid who has broken a ten apart a dozen times on screen has something to attach the written shortcut to.
The mistakes we expect
A wrong tap in the app gets a cue that names the mistake behind it, not a red X. In this stretch of the curriculum, the same handful of errors come up again and again:
- Off by a ten. The trade happened in the wrong direction, or a ten was created and not accounted for.
- The ones digit copied straight through. A sign that the columns are being read as two single digits instead of tens and ones.
- Subtracting the smaller digit from the larger inside a column. The classic "always take the small one from the big one" move. It has to be caught early, because it produces answers that look plausible.
- Right answer, no idea. Common with counting on. The app's checkpoints keep coming back to the model partly for this reason.
What comes before and after
Grade 1 builds tens and ones and works within 20, so a first grader arrives with the idea that a teen number is a ten and some ones. Grade 2 spends its time making that idea do work with bigger numbers. Grade 3 then takes the same regrouping into three-digit addition and subtraction for fluency, and stops treating it as a topic at all — by then it is just how numbers behave.
Try it at the kitchen table
- Bundle straws, pennies, or LEGO bricks into groups of ten. Add 47 + 25 with the bundles first, and let the trade happen in their hands before it happens on paper.
- Ask "which ten did we break?" during subtraction. If they can point at it, they own the idea.
- Watch for answers that are off by exactly ten. That is a regrouping error, not a fact-fluency problem, and it needs a different fix.