How to Help Your Child With Subtraction

My daughter could do "take away" problems in her head all through first grade, so subtraction never landed on my worry list. Then a second-grade worksheet came home with 42 minus 17 answered as 35, and below it 63 minus 28 answered as 45. She was not guessing. She had a method, and it was perfectly consistent: look at the ones, subtract the little digit from the big one, then do the tens. Nobody had shown her that when the top digit is too small, you do not just flip the problem around. You trade.

If your child breezes through single-digit subtraction and then falls apart on two-digit problems, or writes answers that are somehow always a little off, you are almost certainly looking at a borrowing gap, not a subtraction gap. It is one of the most common soft spots in early math, and it is fixable. Here is what got our kitchen table unstuck.

How to help my child with subtraction

Subtraction is not one skill, it is two. There is the plain kind, where every digit on top is big enough to take the bottom digit away, and there is the regrouping kind, where a top digit is too small and your child has to borrow from the next place over. Almost all the trouble lives in the second kind. So the move is to separate them. Make sure your child is solid on the no-borrow problems first, then teach borrowing as what it actually is: unbundling one ten back into ten ones so you have enough to subtract. Do it with real objects your child can hold before you ever touch the written steps. Meaning first, notation second, and the wrong answers start to disappear.

The mistake almost every kid makes

Watch for the answer that is close but wrong, and you will usually find the same thing underneath: the child subtracted the smaller digit from the larger one no matter which was on top. Teachers call it the smaller-from-larger bug, and it is so common it is almost a rite of passage. For 42 minus 17, your child sees a 2 and a 7 in the ones column, subtracts the small from the big out of pure habit, writes 5, then does 4 minus 1 and lands on 35. The real answer is 25.

This is not carelessness, and it is not a sign your child is bad at math. It is a child who learned subtraction as "take the little number away from the big number" and was never shown that the order matters, or that a too-small top digit means you trade. Once you see the pattern, you know exactly what to teach, and it is one specific idea: borrowing.

Borrowing is just trading, run backward

Here is the whole thing, and it is worth teaching with objects rather than words. Build the top number out of bundled tens and loose ones. For 42, that is four bundles of ten held with rubber bands and two loose singles. Now try to take away seven ones. There are only two loose. You cannot do it. So your child unbundles one of the tens, snapping the rubber band, and those ten sticks join the two already there. Now there are twelve ones, easily enough to take seven from, and one fewer bundle up top. Five ones left, three tens left: 25.

That is borrowing. Not a rule, a trade. It is the exact mirror of what happens when you carry in addition, where ten loose ones get bundled into one new ten. Show the unbundling a few times and the written version stops being mysterious: crossing out the 4 to make it a 3 and turning the 2 into a 12 is just a picture of the trade your child already did with their hands. A kid who has seen the trade can rebuild the step when they forget it. A kid who only memorized "cross it out and add a one" has nothing to fall back on.

Why it rests on place value

Borrowing only makes sense if your child truly believes that one ten is worth ten ones. That is a place-value idea, and it is why so many subtraction gaps are really place-value gaps in disguise. If the digits in 42 are just "a 4 and a 2" to your child rather than four tens and two ones, then breaking a ten into ten ones is meaningless, and borrowing becomes a magic move performed on symbols. Ten of these makes one of those, in both directions: that single trade is what carrying and borrowing both are. Shore up the grouping underneath and the subtraction stops wobbling.

The zero trap

The hardest subtraction problems are the ones with a zero to borrow across, like 402 minus 178. Your child needs ones, but the tens place is a zero, so there is nothing there to break apart. The fix is to borrow one step further: trade a hundred for ten tens first, which fills the empty tens place, and then trade one of those tens for ten ones. With bundled objects this is obvious, because your child physically has to go get a hundred-flat and swap it for ten ten-rods before they can make change for the ones. On paper it looks like a chain of crossed-out digits, and kids who only memorized the single-borrow steps freeze here. If your child stalls specifically on problems with a zero in the middle, that is your signal that the trade is being memorized, not understood.

Practice without turning it into a fight

The part parents get wrong most, myself included, is drilling before the trade is solid. A page of borrowing problems a child cannot picture does not teach subtraction. It teaches that math is a thing that makes your stomach hurt, and that lesson sticks for years. Fluency should grow out of understanding, not get forced ahead of it. So keep the reps short, real, and frequent:

• Split the two kinds. Do a few no-borrow problems, then a few that need a trade, and ask your child which ones needed borrowing and how they knew. Naming the difference is half the skill.
• Make change with real coins. Buying a 68-cent item with a dollar is subtraction with regrouping your child already does in the world. Ten pennies for a dime, ten dimes for a dollar, run backward.
• Keep sessions to five minutes. Two short reps a day beat one long grind, and they do not sour the whole subject.

When your child gets one wrong, you do not have to jump in with the answer. Ask, "how could you check that?" Adding the answer back to the number they subtracted is a built-in check, and it turns a red mark into a puzzle. That is the growth-mindset move: praise the reasoning and the effort, not the speed. Carol Dweck's research on praising strategy over ability is worth keeping in mind here, because subtraction is exactly the kind of skill where a child can decide too early that they are "just not good at it." Solid recall of the basic facts helps too, which is why math fact fluency and clean borrowing tend to grow together.

Figure out where the gap really is

The nice thing about teaching subtraction from the trade up is that a miss tells you where the gap is. If your child subtracts the smaller digit from the larger no matter the position, they have not learned that borrowing exists. If they can borrow once but freeze on a zero in the middle, the trade is being memorized rather than understood. If they cannot show you what ten ones and one ten have to do with each other, the gap is place value underneath. Different gaps, different fixes, and you can only tell them apart by watching the reasoning.

It is also worth getting an outside read now and then, because a single homework sheet is a small, noisy sample. Test My Kid is a free, eight-minute adaptive assessment for math and reading, grades K through 8, calibrated to the same NWEA MAP and iReady benchmarks schools use. It reports which topics are solid and which are shaky, so you can see whether subtraction is an isolated soft spot or part of a wider pattern. If it looks like more than subtraction, the signs your child is struggling in math are worth a read too.

My daughter still slows down on the borrowing problems. But now the slowing down is her breaking a ten apart in her head and checking that the trade makes sense, not flipping the digits and hoping. The math never got easier. She just stopped seeing a row of symbols and started seeing tens and ones she knows how to trade.