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The last ten minutes of an exam are often wasted. Some students sit back and wait. Others start redoing a long problem from scratch and run out of time halfway through. A better use is a fixed checking order, decided in advance, that puts the quickest, most valuable checks first.
Should you change answers when you check?
Many students follow the rule "never change your first answer". The research disagrees. In a 2005 paper in the Journal of Personality and Social Psychology, Justin Kruger, Derrick Wirtz and Dale Miller noted that virtually all research on answer changes in multiple-choice tests points the same way. Most answer changes go from incorrect to correct, and people who change answers usually improve their scores.
Why does the myth survive? Their explanation is that changing a right answer to a wrong one causes more "if only" self-blame than sticking with a wrong answer. So those cases stick in memory.
That does not mean you should change answers on a whim. It means a change backed by a specific reason is worth making, such as a calculation error you found or a word in the question you misread. If the exam has negative marking, weigh a change the same way you would weigh any attempt; see negative marking: when is guessing worth it?
The priority order
Work down this list and stop wherever time runs out. The items at the top are worth the most per minute.
Recording (1 to 2 minutes). Check that every answer you meant to give is actually recorded. On an OMR sheet, that means bubbles filled fully in the right row. On a computer-based test, it means responses saved. In written papers, check that question numbers are labelled correctly. An answer you worked out but did not record scores nothing.
Flagged questions you can finish (3 to 4 minutes). Go back to questions you marked as "nearly done" or "unsure between two options". Do not start ones you skipped because they were too long.
Re-read the question stems (2 minutes). Look for words like "not", "incorrect", "except" and "maximum", and for the unit asked for (cm or m, mol or g). Misreads are common and quick to fix.
Quick checks on numericals (2 to 3 minutes). Do not solve them again. Use quick tests instead. Do the units match? Is the sign sensible? Is the size plausible? Does a limiting case work?
Only then, anything else. If time remains, look at a question you skipped.
Quick checks in practice
These checks take seconds:
Units: an energy answer should come out in joules, not newtons. See dimensional analysis as a 30-second check.
Sign: a body slowing down has acceleration opposite to its velocity, and an exothermic reaction has a negative ΔH.
Size: a person's walking speed should be a metre or two per second, not hundreds.
Limiting case: if friction becomes zero, does your expression reduce to the frictionless answer?
Plug back: for an equation you solved, substitute the root into the original.
These catch many slips without redoing the whole problem.
Making ten minutes exist
Checking only works if you leave time for it. A two-pass approach helps: answer what you can quickly, mark the rest, then come back. Our guide to time management in the exam hall explains it in detail. Aim to finish your last pass with about ten minutes on the clock, and treat that time as reserved.
Practise it before it counts
In each practice test, note which check found an error. After a few tests you will see your own pattern. Maybe you misread "not", or you drop signs in electrostatics. Move that check higher up your list.
When you review a numerical you got wrong, compare your working line by line with a full solution to see exactly where it went off. The Fermi Problem Library has a step-by-step solver that explains the reasoning, which helps with that comparison.
