For teachers · September 11, 2026

Error Analysis in Math: Teaching Kids to Find Mistakes

Error analysis in math means giving students a worked problem with a mistake in it and asking them to find it, name it and fix it. It works because most mistakes aren't random: forgetting to carry, lining up decimals by their right ends and adding denominators are predictable, and a student who can explain one of those errors in someone else's work is better placed to catch it in their own. You can start in first grade with two answers and one question: who is correct?

Why error analysis in math is worth ten minutes a week

Most practice asks students to produce an answer. Error analysis asks them to evaluate one. That shift matters for three reasons.

First, it puts the misconception itself on the table. A page of addition with regrouping practices the procedure. A problem where someone forgot to carry makes students look straight at the step that goes wrong.

Second, it builds reasoning. One of the Common Core Standards for Mathematical Practice, MP.3, is about making arguments and critiquing the reasoning of others. "Theo is wrong because he counted the 8" is a small version of exactly that.

Third, it feels safe. The mistake belongs to a fictional student, so nobody is embarrassed. Kids who hesitate to share their own work will often happily explain someone else's.

Three levels of error analysis math problems

Error analysis gets harder in a clear sequence. Use it to match the task to the student.

Level	The task	Sentence frame
1. Spot it	Two students give different answers. Who is correct?	"[Name] is correct because..."
2. Name it	One worked solution with a wrong answer. What mistake was made?	"The mistake is that..."
3. Fix it	Explain the mistake, then show a correct method.	"The mistake is... A correct way is..."

The "Who is correct?" pages in the Math Practice Library follow this sequence for every grade. The Support page asks which of two students is right, the On Level page asks students to name the mistake, and the Challenge page asks them to explain it and then show a correct method.

In the second-grade version above, the Support page opens with "Felix says 31 + 39 = 70. Theo says 31 + 39 = 60. Who is correct?" (Felix.) The On Level page shows Rosa's work on 45 + 19: "ones: 5 + 9 = 14, wrote 4; tens: 4 + 1 = 5." The answer should be 64, and students have to explain that Rosa didn't carry the 1 ten from 14.

Error analysis examples for grades 1-5

Each grade has its own predictable mistakes. Here is one real problem per grade from those pages.

Grade	The worked mistake	What went wrong	Correct answer
1	Theo works out 8 + 5 by saying "8, 9, 10, 11, 12," so 12	Counted the 8 as the first count instead of starting at 9	13
2	Priya works out 31 + 39: tens 3 + 3 = 6, ones 1 + 9 = 10, writes 610	Wrote both column totals side by side instead of regrouping	70
3	Omar works out 4 × 9 by skip counting 4, 8, 12 ... up to 40	Skip counted 10 groups of 4 instead of 9	36
4	Lena works out 443 + 265: tens 4 + 6 = 10, writes 0 and doesn't carry	Didn't regroup 10 tens as 1 hundred	708
5	Rosa works out 8.5 + 0.31 by writing it as 8.5 + 3.10	Lined up the right ends of the numbers, not the decimal points	8.81

A few notes on using them:

Grade 1. Counting on is where this error lives. Have students act it out on a number path: finger on 8, then five jumps. The first jump lands on 9, not 8.

Grade 3. Another third-grade problem reads "Omar worked out 6 × 7 like this: 6 + 7 = 13." That's a different kind of mistake (adding instead of multiplying). Ask students to sort errors into "slip" mistakes, like losing count, and "wrong idea" mistakes, like using the wrong operation.

Grade 5. The fifth-grade page also includes fraction errors such as "2/3 + 1/2 = 3/5," where the student added numerators and denominators. The correct sum is 7/6. A useful follow-up: "Can adding two positive fractions give an answer smaller than one of them?" Since 3/5 is less than 2/3, the answer can't be right, and a student can spot that without finding a common denominator.

How to run an error analysis routine

A predictable routine keeps it to about ten minutes.

1. Show the work, not just the answer. Levels 2 and 3 need visible steps. Write them the way a student would.
2. Give silent think time. One minute, no talking. Students can mark the step they think went wrong.
3. Turn and talk. Partners use the sentence frame for the level you're working at.
4. Share one or two explanations. Listen for precise language: "didn't carry the ten" beats "did it wrong."
5. Fix it together. Solve it correctly, then ask how the student in the problem could have caught the mistake by estimating. For Lena's 443 + 265, about 400 + 300 = 700 shows that her answer of 608 is too small.

Then give students two or three problems to try on their own.

Making your own error analysis math worksheet

If you're building an error analysis math worksheet yourself, a few rules keep it useful:

• Use plausible mistakes. Pick errors students actually make: forgetting to regroup, counting the starting number, misaligning place value. A random wrong answer teaches very little.
• One error per problem. Two errors at once make the task confusing.
• Show steps for Levels 2 and 3. "Felix says 7 × 7 = 56" is fine for spotting, but naming a mistake needs visible work.
• Mix in some correct work. When students know a worked example might have no error at all, they have to check rather than assume.
• Use made-up names, never a student from your class.
• Write the named mistake in the answer key, not just the right number, so students can compare explanations.

Your own class's work is a good source of mistakes. Yesterday's wrong answers make today's error analysis, and exit tickets collect them for you. Our guide to math exit tickets explains how to sort a class set quickly.

The Challenge page above asks for both parts at once. One problem reads: "Malik worked out 4.9 + 0.63 like this: 4.9 + 0.63 written as 4.9 + 6.30. Explain Malik's mistake, then show a correct method." The answer key names the mistake (he lined up the digits by their right ends instead of the decimal points) and gives a correct method: line up the decimal points, so 4.9 + 0.63 = 5.53.

Common pitfalls

Making it about who's wrong. Keep the tone curious: "What was Omar thinking?" Most errors come from a reasonable idea used in the wrong place.

Jumping straight to Level 3. Explaining a mistake in writing is hard. A student who can't yet say who is correct won't be able to write the explanation. Build up through the levels.

Doing it once. Error analysis gets better with repetition. A regular weekly slot turns it into a habit students bring to their own work.

Never connecting back. After the routine, ask students to check one problem in their own work for the same mistake.

If your class spans a range of levels, how the three levels work shows what changes between Support, On Level and Challenge pages. You can browse the 2nd grade math worksheets or print the free 16-page sampler. Error analysis cards also make a good task for early finishers in math.

Frequently asked questions

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