The most common mistake in mock season is volume without spacing. Students sit five papers in a fortnight, receive five sets of feedback, and act on none of them because there is no time between them to re-learn anything.
November to December
One full paper per subject, sat properly, marked externally. The purpose is a baseline and a topic map, not a grade. Use the topic percentages to write a ranked list of weaknesses per subject and put it somewhere visible.
January to February
Topic tests only. Work down the ranked list, one topic at a time, re-testing each about ten days after the first attempt. This is where the grade movement actually happens, and it is the phase students skip.
March onward
Return to full papers under strict timing, now to build stamina and exam-day pacing rather than to diagnose. Two per subject, spaced a fortnight apart, is enough.