This method gives your teen focus
Your teen has a heck of a lot of material to go over during their study break.
Realistically, there is not going to be enough time to study and memorize every single thing their teachers have said over the past year. Trying to do so is not making good use of the precious time your teen has to study.
Trying to learn EVERYTHING is a fruitless actually detrimental exercise. It will make your teen stressed, make them loose confidence in themselves, and worst of all, will stop them from properly learning and absorbing what really matters.