Sitting a practice test is the easy half. The score at the end is a measurement, and a measurement on its own changes nothing. What changes the next score is what is done in the two hours after the paper is put down.
Sorting errors by cause
Every wrong answer belongs to one of four causes: the topic was not known, the topic was known but the question was misread, the method was right and the arithmetic failed, or time ran out.
These four require four different responses. Studying the topic again fixes the first and does nothing for the other three, which is why a student can revise for weeks and watch the same score return.
The correct answers that were guessed
A question answered correctly by elimination or by chance is not a question the student can do. It will appear again in a form where the guess does not work.
Marking uncertainty during the test, with a single dot beside the question, turns these into visible items afterwards. Without the mark they disappear into the score.
Reworking before reading the explanation
The explanation is convincing while it is being read and forgotten shortly after, because reading is not the same as solving. The question is worked again from a blank page first, with unlimited time.
If it comes out on the second attempt, the cause was time or attention. If it does not, the cause is the topic. This single step separates the four causes more reliably than any other.
Keeping a running record
A short list, one line per error, with the question, the cause and the correction. After three tests the list stops being a list and becomes a pattern: the same two or three causes account for most of the loss.
Preparation then aims at those causes rather than at the syllabus as a whole, which is where the visible gains come from.
How often to sit one
Weekly is enough for most students, and more than weekly usually reduces the quality of the analysis. A test that is not analysed properly has produced a number and consumed a morning.
The ratio to hold is simple: time spent on analysis should be at least the time spent on the test.