The Wall Most P2 Kids Hit Around Term 2
For a lot of Singapore children, Primary 2 is the year maths stops being easy. They cruised through P1. Number bonds clicked, addition within 100 felt fine, even simple subtraction was no trouble — `28 - 5`, `49 - 7`, all of it landed. Then around Term 2 the worksheets change, a problem like `42 - 17` appears, and the wheels come off.
You see it in the homework. The child stares at `42 - 17`, the pencil hovers, and then they write `35`. Confidently. They looked at the ones column, saw 2 and 7, and did the only thing that made sense: took the small one from the big one. Seven minus two is five. Forty minus ten is thirty. Thirty-five. Done.
It is wrong, but it is not careless. It is a child applying a perfectly reasonable rule that happens to be the wrong rule. This is the regrouping wall — what older Singaporeans still call "borrowing" — and it is the first place in primary maths where a child cannot bluff their way through on instinct.
The good news: this wall is climbable, and the children who get over it cleanly are not the ones who memorise the fastest. They are the ones who understand what the digits actually mean. That is the whole story here.
Place Value Is the Real Lesson, Not "Borrowing"
Start with the vocabulary, because it matters more than it looks. Most of us were taught to "borrow" — you borrow a one from the tens column and pay it back somehow, the language fuzzy, the loan terms never explained. MOE's current syllabus deliberately uses regrouping instead, and the change is not just fashion. "Borrow" suggests something is taken and returned. Nothing is returned. What actually happens is that a ten is traded — broken open into ten ones that join the ones already there.
If your child says "I borrowed a one," gently reframe it: "You changed one ten into ten ones." It sounds pedantic. It is not. A child who thinks they "borrowed a one" often believes they moved a single unit, which is exactly why so many forget to reduce the tens. The old word was hiding the mathematics.
Here is the thing most tuition drills get backwards. They teach the steps — cross out the 4, write a small 3, carry a 1, subtract — as a sequence to memorise. A bright child can memorise it and pass the topic test. Then in P3, when the numbers get bigger and the problems wordier, it falls apart, because they never understood what the small crossed-out numbers meant.
What `42 - 17` actually says is this: I have 4 tens and 2 ones, and I want to take away 1 ten and 7 ones. The tens are easy. The trouble is the ones: I only have 2, and I am asked to remove 7. I cannot. So I reach over to my 4 tens, take one, and break it into 10 ones. Now I have 3 tens and 12 ones. Twelve ones take away seven is five. Three tens take away one ten is two. Twenty-five.
Notice the procedure falls out of the understanding. A child who genuinely sees `42` as "four tens and two ones," and knows one ten can be swapped for ten ones, will reinvent the steps on their own — because the steps are just the obvious thing to do. The procedure is a consequence of place value, not a replacement for it.
This is why I always start with objects, never the written algorithm. The written method is the summary; the understanding has to come first, in the hands.
Base-Ten Blocks and the Bundling Idea
The single best tool for this is base-ten blocks: little unit cubes for ones, and rods (sticks of ten cubes joined together) for tens. You can buy a set cheaply, or you can fake it brilliantly with things from around the flat.
The fake version I like best: straws and rubber bands. Bundle ten straws together with a rubber band — that bundle is a "ten". Loose straws are "ones". Now `42` is four bundles and two loose straws, sitting on the table where the child can touch them.
To do `42 - 17`, you tell the child to take away 1 bundle (one ten) and 7 loose straws (seven ones). Taking the bundle away is easy. Then they go to take 7 loose straws — and there are only 2. They are stuck.
This is the magic moment. You ask, "You have bundles right there. What could you do?" Sooner or later the child realises they can snap the rubber band off one bundle, turning it into 10 loose straws. Now there are 12 loose straws. Take 7 away, 5 remain. The bundles left: 3 minus the 1 they removed earlier is 2. Twenty-five.
The child has just done regrouping with their hands. The rubber band coming off the bundle is the ten being broken into ones.
When they later see the written method — crossing out the 4, writing 3, putting a little 1 in front of the 2 — it is no longer a magic ritual. It is a picture of the thing they did with the straws.
Egg cartons, paper clips on a chain, ten-frames from their P1 days — all of these work. The specific objects do not matter. What matters is that a ten is something you can physically break into ten ones, and the child sees that with their own eyes before they ever touch the algorithm.
The Three Errors You Will Actually See
When you sit with your P2 child's subtraction homework, you will see the same handful of mistakes over and over. They are predictable, and each points at a specific gap.
Error one: subtracting the smaller digit from the larger, regardless of position. This is the `42 - 17 = 35` mistake from the top of this post. The child treats each column independently and always takes small-from-big. It feels right because in P1, the top digit was always bigger. The fix is not "remember to regroup" — it is going back to the bundles so the child feels that you genuinely cannot take 7 ones from 2 ones without breaking a bundle. The error is a place-value gap wearing a procedure costume.
Error two: regrouping but forgetting to reduce the tens. The child correctly turns 2 ones into 12 ones, does `12 - 7 = 5`, and then does `4 - 1 = 3` in the tens — forgetting they already used one of those tens. They get `35` again, by a completely different route. This child understands regrouping but is treating the borrowed ten as free. With the straws: once a bundle is unbundled, it is gone from the bundle pile. Make them physically move it. The tens column has to shrink because a ten literally left.
Error three: regrouping when it is not needed. Give the child `48 - 23` and some will dutifully regroup anyway, because the last ten problems all needed it and they have stopped reading the actual numbers. `8 - 3` needs no regrouping. This is a reasoning failure, not a procedure failure: the child has switched off the question "do I have enough ones?" and gone onto autopilot. The cure is mixing regrouping and non-regrouping problems on the same page so the child must check every time.
If you can name which of these three your child is doing, you are most of the way to fixing it. The error tells you the gap.
And there is one habit that catches all three before they reach the page: estimate before, sanity-check after. Before working out `42 - 17`, ask your child roughly what the answer should be. Forty-something take away not-quite-twenty lands somewhere around twenty-five. They do not need the exact number — just a ballpark. Then, when they finish and write `35`, the ballpark catches it: thirty-five is too big, something went wrong, go back and look.
The way to teach it is to round both numbers to the nearest ten together — `42 - 17` becomes roughly `40 - 20`, so the answer should be around twenty, a little more. When the real answer (25) lands near the estimate, you both nod. When it lands far away (35), you both frown and check. Make the frown a habit; the frown is the skill.
This is not extra work — it is the difference between a child who blindly trusts whatever their pencil produced and one who has a felt sense of whether a number is plausible. Singapore's PSLE, years away but built on exactly these habits, is full of multi-step problems where a single unchecked subtraction error cascades into a wrong final answer.
Home Practice: Objects First, Then Numbers
Here is a concrete week-by-week way to build this at home. None of it needs a worksheet pack and none of it takes more than ten minutes a sitting.
- Days 1-3: bundles only, no writing at all. Straws and rubber bands. You call out a subtraction the child acts out entirely with bundles and loose straws. No pencil touches paper. The goal is purely that breaking-a-bundle moment becoming familiar and obvious. Do five or six a day.
- Days 4-6: bundles beside the written sum. Now the child does the straws and writes the standard column method next to them, watching how the crossed-out tens digit matches the bundle they unbundled. The straws explain the squiggles. Keep some problems that need no regrouping in the mix so they keep reading the numbers.
- Days 7-9: written first, straws as a check. The child tries the column method on paper first, then verifies with bundles only if they are unsure or got a surprising answer. The objects become a safety net rather than the main event.
- Day 10 onward: numbers only, with estimation. Pure written practice, but every single problem starts with "roughly what should this be?" and ends with "is that reasonable?" The bundles stay in the drawer, available if a wall appears.
Keep the numbers small and two-digit for now. `52 - 28`, `61 - 34`, `70 - 45`. The "minus from a tens number" cases like `70 - 45` are worth extra reps, because regrouping from a zero in the ones is its own little hurdle and trips up plenty of children.
If you do just one thing this week, do this. Tonight, make four bundles of ten and leave two straws loose — that is `42` on the table. Tell your child you want to give away 17, and let them work out, in their hands, that they will have to break a bundle to do it. Do not correct, do not rush; let the stuck feeling sit until they reach for a bundle themselves.
Do that for three nights with no pencil at all. Then, on the fourth night, write the column sum next to the straws and show how the crossing-out matches the breaking. By the end of a week, the regrouping that looked like a wall starts looking like the obvious thing — because, with a ten you can physically break apart, it is the obvious thing.
How This Connects to Everything Coming Next
It is tempting to treat regrouping as one topic to clear and move past. It is not. It is a foundation the rest of primary arithmetic sits directly on top of.
In P3, subtraction extends to three- and four-digit numbers, and the child may have to regroup across two columns at once — `403 - 158`, where you regroup the tens and the ones, cascading through a zero. A child who only memorised the two-digit steps stalls here. A child who understands trading tens for ones extends it to trading hundreds for tens without blinking.
The same place-value logic powers column addition with carrying, the mirror image — ten ones bundled up into a ten instead of a ten broken down into ones. Get regrouping and the child has secretly already understood carrying. Later still, the same idea underlies long division and the borrowing inside money calculations ($10.00 - $3.45 is regrouping wearing a dollar sign). The trading-between-places idea never goes away; it just gets dressed up.
This is why it is worth slowing down at P2 and doing it properly with objects, even when a faster memorise-the-steps route would pass next week's topic quiz. The proper version compounds. The shortcut version has to be relearned, painfully, every time the numbers grow.
Red Flags Worth Acting On
Most struggle here is normal and passes within a few weeks of the right practice. But a few patterns tend not to self-correct, so it is worth catching them:
- Gets regrouping right one day, completely lost the next. Usually means the procedure was memorised, not understood — it evaporated overnight because nothing was anchoring it. Go back to bundles for a few days. Understanding does not evaporate the way memorised steps do.
- Can do it with straws but freezes the moment it is pure numbers. The bridge from concrete to abstract has not formed. Spend longer in the middle stage where the straws sit beside the written sum, so the link is visible.
- Always gets the answer too big. Almost always the "forgot to reduce the tens" error. Watch them work and check that the tens digit actually shrinks when they regroup.
- Refuses to estimate, insists on computing straight away. Not a maths gap but a habit gap, and the one most worth fixing because it protects against every future careless error. Make the ballpark guess non-negotiable, every single time, until it is automatic.
- Genuine distress and tears at the topic, beyond ordinary frustration. Stop the worksheets for a week. Do bundles only, no writing, no right-or-wrong pressure — just playing with breaking tens into ones. Rebuild the confidence on the concrete level before going near the page again. The tears usually come from the abstraction, not the maths.
The One-Sentence Version
Regrouping is not a borrowing trick to memorise — it is the moment a child learns that one ten can be traded for ten ones, and once they have felt that in their hands with a broken bundle of straws, every column subtraction, every carry, and every multi-digit sum for the rest of primary school is just the same idea wearing a bigger number. Teach the meaning, and the procedure teaches itself.
For families who want that concrete-pictorial-abstract sequence built into structured digital practice — base-ten visuals, regrouping animations, and estimation checks woven into every problem the way P2 actually needs — BrightBit's P2 Maths module is sequenced place-value-first rather than procedure-first.