The standard revision advice is to work through past papers and mark them against the published mark scheme. It sounds rigorous. In practice it is the single most over-rated revision activity in GCSE preparation, and the reason is simple: mark schemes are written for people who already know what a correct answer looks like.
When we compare a student's self-awarded mark against an examiner's mark on the same script, the student is on average seven marks generous on a Maths Higher paper and closer to eleven on English Language Paper 1. That gap is not carelessness. It is the difference between recognising an answer and producing one.
Where the marks actually go
Mark schemes award method marks for a specific route through a problem, not for arriving somewhere near the answer. A student who reads 'M1 for correct substitution' will tick their own working if the numbers look roughly right. An examiner checks whether the substitution was written down at all.
- Unshown working: the answer is right, the method marks are not awarded.
- Premature rounding: a correct method loses the accuracy mark at the last line.
- Nearly-right terminology in science: 'the particles move faster' where the scheme requires 'the mean kinetic energy increases'.
- In English, describing a technique rather than analysing its effect, the AO2 boundary students cross without noticing.
What to do instead
Sit fewer papers and get more from each one. Two papers marked properly, with the errors categorised and re-tested a fortnight later, beats six self-marked papers every time. The point of a practice paper is not the practice, it is the diagnosis.
If you are going to self-mark, do it in two passes: first mark it as generously as you like, then go back and cross out every mark where the working is not physically written on the page. The second number is closer to your real one.