Summer is the highest yielding period in exam preparation, and the reason is the calendar rather than motivation: there is no load of school assessments and submissions.
Where the gain comes from
During term, preparation collides constantly with school assessments and retreats at every collision. In summer that tug of war does not exist.
The second gain is being able to work in long blocks: a full length practice test takes a whole Saturday during term and can be part of the daily flow in summer.
The two things summer is best used for
The first is closing foundations: for a student with content gaps that work does not fit into term time and can be closed over the summer.
The second is the practice and analysis cycle: working several full tests back to back and analysing them makes the error pattern visible, and the term programme is then built on that pattern.
The burnout line
A programme that fills the whole summer produces a student who starts September tired. The school year runs nine months and the real load is there.
The criterion is this: can the pace set in summer be sustained during term. A pace that cannot be sustained gives back in September what it gained in summer.
What not to do in summer
Trying to finish over the summer the whole of a topic that will run through the year. Where the content will be taught again at school, what was learned in summer fades by September.
Instead, summer targets the parts that will never be taught at school or that are already behind.
For which student
For a student with a large gap between the current score and the target, summer is the only period that makes closing it possible.
For a student with a small gap, summer is not obligatory; a steady pace during term can be enough. That distinction is made by measuring rather than assuming.