There are three essential steps to any good math exam prep and they should be done in this order:
1. Review PAST MATH TESTS
First, your son should review his past math tests which is the math from earlier in the term. Reviewing and re-writing past math tests is an excellent refresher since he has already seen and done these tests, plus it highlights the math concepts he has had difficulties with. The math concepts he finds easy will be reinforced by re-writing these tests, and the concepts he finds difficult are the ones he needs to focus his attention on and strengthen.
2. Work through the EXAM REVIEW SHEETS
Second, he should work through the exam review sheets which are a summary of the whole course provided by his math teacher. Doing so should help strengthen his understanding of the math concepts he finds challenging. In addition, it should also give him a fairly good idea of what to expect on the exam.
3. Write an OLD EXAM
Third, he should write an old exam in order to test his understanding by doing something he has not seen before. Many teachers have old exams they give to students for exam prep purposes, if asked. Note: He should approach writing the old exam as though it's a mock exam. In other words, if the upcoming exam will be 2 hours long then he writes the old exam over a 2 hour period of time, without a break, as though it was a real exam. Then, of course, he should get some feedback on how he did on the old exam.
WHEN to start exam prep
Exam preparation should start at least a week, or more, before the exam but how much or little prep work your son needs to do depends on his overall understanding of the course material. The key point is that it's not possible for anyone to prep effectively by cramming the night before the exam. See When should my son start studying for his exam.
Avoid this BIG mistake
The biggest mistake I see students making when studying for an exam, especially weaker students, is they jump into doing the exam review sheets first. The problem with this approach is that the student is attempting math questions he hasn't seen in months so the odds are high he won't remember how to do some, or much, of the math. Instead, if he first starts with a review of past math tests, which serves as great math refresher, that, in turn, sets him up for much better success and understanding when he does the exam review sheets as a second step in his exam prep. In other words, doing the exam review sheets first is often an extremely frustrating and discouraging experience which can increase the student's stress about the upcoming exam and which often leads to a sort of panicky last minute attempt at memorization of the course material which unfortunately is not a recipe for exam writing success.