Diagnose first, then target misconceptions with a simple four-step routine as part of concept repair
Two students produce the same wrong answer. The instinct is to fix them in the same way. But the same wrong answer doesn’t mean the same problem.

A car starts from rest and reaches 20 m/s in 5 s. Calculate the acceleration. Student A writes 8 m/s². Student B writes 5 m/s². Both are wrong, but the typical response is identical: reteach everything indiscriminately, show a model answer or infer the mistake from the answer. But these answers represent different problems. One student may have chosen the wrong equation; another may not understand what from rest means. A third may simply have made an arithmetic slip.
This is the idea behind concept repair: diagnosing the cause of an error before deciding how to respond. In practice, I use a simple diagnostic routine built around four stages: meaning, method, apply and execute.
A full reteach could have taken the entire lesson; a targeted repair only took 10 minutes
1. Meaning: what does this represent?
1. Meaning
First, I check whether students have an understanding of the foundational aspects of the question. Do they know what rest means, which value represents initial velocity and the units for time? If students lack this basic knowledge, reteaching at a different point will not help.
2. Method: which approach fits?
2. Method
If the meaning is secure, I move on to checking the method. I do this by asking the following questions: ‘Using your equation sheet, which equation would you use if you know velocity and time?’ or ‘Which equation matches the information given in this question?’. If students are unsure here, the issue is that the method isn’t secure.
3. Apply: can they substitute correctly?
3. Apply
If both meaning and method are secure, I then check their ability to apply the method to the question. In the acceleration example above, I ask students to talk me through what they are putting in for each symbol. At this stage, common issues appear quickly – such as the values being swapped or units being ignored.
4. Execute: can they calculate and check?
Finally, I check execution. At this stage, errors are usually simple such as arithmetic mistakes, not checking that answers are sensible or even misuse of the calculator due to maths anxiety or uncertainty. Here, the students’ issue is likely performance, which is usually repaired with stabilisers such as ‘Redo the final step’, ‘Does your answer seem sensible?’ and ‘Are the units correct?’.
4. Execute
Finally, I check execution. At this stage, errors are usually simple such as arithmetic mistakes, not checking that answers are sensible or even misuse of the calculator due to maths anxiety or uncertainty (rsc.li/3SxDq5K). Here, the students’ issue is likely performance, which is usually repaired with stabilisers such as ‘Redo the final step’, ‘Does your answer seem sensible?’ and ‘Are the units correct?’.
Diagnose in order and stop at the first break
Diagnose and stop
The key discipline is to diagnose issues in order and stop at the first break. The first failure reveals exactly what needs to be repaired. In one class, most students didn’t even attempt the acceleration question, and the temptation would have been to do a full reteach. Diagnosis instead showed that many pupils were unsure of when to use the correct acceleration equation: a = (v-u) / t or v2 - u2 = 2ax. You can then specifically target repair at the method used rather than being broad and imprecise. A full reteach could have taken the entire lesson; a targeted repair only took 10 minutes.
Why it matters
In busy classrooms, the issue is rarely effort, it’s precision. By diagnosing first, the repair changes depending on where the chain breaks. A student missing the meaning needs something different from a student who has the method but misapplies it.
Pitfalls to avoid
Resist the urge to jump to reteaching too quickly. This often costs valuable time and can increase cognitive load while dampening focus. Another common pitfall is diagnosing out of order: for example, if you check the method before meaning, you risk masking the issue. The sequence matters.
The same wrong answer can have different causes, and different causes require different responses. The first step is finding the break in the chain; the next is using that location to determine the fix. Diagnosis isn’t preparation for teaching – it is the teaching.
Michael Prince






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