Maths-wise, this is what I often do with my Y11 students. We mainly work with past papers (especially close to the exams if no new topics are needed to learn/revise).
It is a good strategy but I'd advise 2 things:
1 - how to approach the past paper
2 - when and how to use extra resources
1 - At this stage (Y11), timing the paper is quite important. So the student should have set time (either standard 90 mins or more if allowed due to SEN, etc. - you would know by now how much extra time, if at all, is your child allowed, usually it's +25%).
Prior to starting with any paper, the student should look at any "problematic" topics and revise a bit, then set a timer a work their best.
Specific exam techniques aside (I'm not going to add those as that would make a way too long message), when the time if out and there are perhaps some more questions left, grab another pen colour (or note clearly which questions were done overtime) and finish all that's possible.
Then and only then there's time to look at the mark scheme and:
- check the answers (attempt to correct them by using the mark scheme - make notes whether you/the student understands it now - again, ideally in another colour "marking/correction" colour so it's clear what was independent work and what was done with help)
- look at any problematic questions and try to understand the process by looking at the mark scheme a re-working it in your own terms.
This would give the student an idea what needs to be practised as the next step, before doing another past paper.
Which takes us to:
2 - In addition to past papers, it's certainly good to add extra resources. Depending on the exam board, it's best to keep to the specific exam board style questions (other exam boards papers and questions might be useful in the rare case one runs out of resources - which is almost impossible with the amount of great textbooks + workbooks and online resources, both free and paid, available for each exam board).
So using the past papers as a baseline for the revision is great when used well but unless one already mastered the whole necessary curriculum, there will likely be extra resources needed too.
This is just for maths, I can't speak for the best exam techniques for other subjects but I can imagine it might be quite similar.
Whew, this IS a long message already =)