Careless mistake or real gap? How to tell

Collect a week of wrong answers and ask your child to redo each one cold. Right straight away means a slip. Slow, or wrong in a new way, means a fact that is not yet known. Wrong in the same way again means a step in the method is faulty.

9 minute read · Updated October 5, 2026

You may recognize this. The test comes home with a mark that does not match the child you know. You have seen them do this. Next to three of the crosses the teacher has written "careless!", and your child shrugs and says they will be more careful next time.

Maybe so. But "careless" covers three quite different problems, and only one of them is cured by care. You can find out which is which with a pencil and about fifteen minutes.

Why does "be more careful" not work?

"Be more careful" fails because it does not tell a child what to do differently. A child who misread a sign can act on "circle the sign first". A child who does not know 7 × 8, or who borrows the wrong way, cannot become more careful at something they have not yet learned.

It also puts the fault in the child and not in the working. Guidance for teachers from England's Education Endowment Foundation says feedback should be "specific and clear, encourage and support further effort, and be given sparingly". "Careless" is none of those. "You added here and the sign says take away" is all three.

What are the three kinds of wrong answer?

For sorting at home, a wrong answer in arithmetic is one of three kinds. A slip is a mistake in something the child can do. A fact gap is a number fact that has to be worked out each time. A method gap is a step in a written method that the child does wrongly every time.

The third kind is easily mistaken for carelessness, because the child is clearly trying and the answers are nearly right. One classic study of children's column subtraction found that many errors came from small, consistent faults in the procedure, which produce the same kind of wrong answer each time. The Education Endowment Foundation's guidance says misconceptions should be "uncovered and addressed rather than side-stepped or ignored".

How do I sort a week of mistakes?

Keep every wrong answer for a week, then sit down once and have your child redo each question without being told what went wrong. Watch how the second try goes, write S, F or M beside it, and count. It takes about fifteen minutes.

Here is how a sorted week might look. These eight are made up to show the pattern.

Eight mistakes that looked like eight separate problems turn out to be three. One step in subtraction, two times table facts, and two true slips. Look at the first two Ms set out in columns:

    6 3         8 1
  - 2 8       - 4 7
  -----       -----
    4 5         4 6

The third M does the same with a zero: 6 − 0 for 0 − 6, where the right answer is 54. That is one faulty step, three times. This child is not careless. They are following a rule that happens to be wrong.

What do I do about slips?

Slips are cut down by habits, not by effort. Give your child one small routine for the kind of slip they make most, practice it until it is automatic, and praise the routine when you see it. Two habits at once is too many, so pick the one that fits the pile.

• Wrong sign read: circle the sign before starting each question.
• Digits swapped or miscopied: say the number aloud while writing it, and use squared paper with one digit in each square.
• Question not read to the end: read it twice, and underline what is being asked for.
• An answer that is far off: estimate first. 342 + 215 is "about 550", so 575 deserves a second look.
• Any calculation: check by doing the opposite. Add the answer back after a subtraction, multiply back after a division.

If the slips pile up in long questions and vanish in short ones, slow facts may be behind them. Ofsted, England's school inspectorate, notes that pupils who cannot quickly recall facts "struggle with calculations due to their working memory being overloaded". A child spending their attention on 7 × 8 has less left for keeping columns straight.

What do I do about fact gaps?

Write down the exact facts that came up as F, and practice only those, a few at a time, mixed in with facts your child knows well. Ask them out of order and turned around. A short session on most days does more for a stubborn fact than one long sitting.

A US federal practice guide written for children who struggle with math recommends "a mix of previously and newly learned material" in practice, so shuffle three missed facts with six safe ones. Our piece on why times tables don't stick has a two-week plan built this way.

What do I do about a method gap?

Find the one step that goes wrong, show your child why it does not work, and practice that step alone on small numbers before returning to full questions. Do not hand out another page of the same sums first. Practicing a faulty step only makes it faster.

For the usual faults in column addition and subtraction, with the wrong and right working side by side, see carrying and borrowing: the slips to look for.

When should I talk to the teacher or a doctor?

Talk to the teacher if a few weeks of steady, specific practice changes nothing, or if the sort shows something wider than a few facts and one step. Bring the sorted pile with you. A doctor or an educational psychologist can assess a child. A parent, a blog or an app cannot.

• Slips stay just as frequent after a month of one clear habit, and show up in other subjects as well.
• Facts practiced in short sessions over several weeks are still gone each Monday.
• Math homework brings on dread or tears that other homework does not.

None of these is a diagnosis. They are reasons to ask. Asking is worth it, because math difficulties can go unnamed: one study of nearly 2,500 children aged 7 to 13 in Northern Ireland found that about 6% met current criteria for a specific learning disorder in mathematics, and only one of them had a formal diagnosis of dyscalculia. Under older criteria the figure would have been 1.1%, so the number depends on the definition used. Our guide to why a child may be struggling with math goes further.

Where Plusy fits

Plusy does a small version of this. After a wrong answer that fits a known pattern, it says what happened, such as "Looks like you added. 7 × 8 is 56." or "Close. The digits are swapped." For a column sum worked in the boxes it names the step, for example "You forgot to borrow. Borrow 1 from the tens".

A missed question comes back once later in the same round. When the same kind of mistake turns up three times in a week, a short practice set for it appears on Home, and the Grown-ups card on the You tab shows one line naming the kind of mistake that has come up most. That one line is all the parent view there is: no report and no charts. See what Plusy does after a wrong answer.

Plusy cannot tell you why a child is struggling. It can show you which step keeps going wrong. Start free, or do the sort above with paper: it needs nothing else.

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