For other students, their trouble spot is further down the line of their study process.
Maybe they do make sure they actually understand what they revise, but when it comes to applying their knowledge to practice questions, they may as well be written in another language.
If this happens to you or your teen, then you are going to have to PRACTICE doing loads of practice questions.
Im sorry theres not a magic wand solution to this one, but practicing questions that mimic those that will be in the exam will be the key for you.
If this is you, do not feel bad. Its one of the most common mistakes students make studying their guts out but omitting to practice applying what they know to a real problem or question.