Teenagers do need support in revising. The frontal lobes are not yet fully developed and as such they know they should be revising, but struggle to actually do it.
Helping them make a plan, from now, to do a little each week in each subject (as little as 5 mins a week is better than nothing) such that they'll practice everything in the course by next May.
Then they need adult help to actually sit down and do it. Withhold the TV remote/their phone/use whatever they enjoy as the reward for getting 5-10 mins of revision done of an evening/morning etc.
As for what to do? The very best thing they can do is to practice what they'll actually be doing in the exams. So past paper questions.
At this stage in y11 that might mean using the revision guide to help them answer the Q. But then more important than having a go is using the mark scheme. They need to worry less about being right, and focus on it being a practice exercise. So looking at the mark scheme and thinking 'where was I on the right track?' and celebrate that, but then also really interrogating it: 'where in the question does it suggest I should give that answer? Where are the clues I should have spotted? What was the knowledge I'm missing for this question? What was the key vocabulary I should have used?'
And then if this is repeated, even just one question a week, they'll get used to recognising what questions are asking them to do, and how to compose the answers.
This is less fun than making posters or mind maps, but those are far less effective. And if you're going to do only 5 mins, it needs to be the most effective 5 mins.
5 mins a week across 10 subjects is less than an hour. Ideally spread out across the week.
Remember something is better than nothing.
Teenagers look like adults but are still children who do need support. (Most of them, some of them do just do it!)
Oh, and these days there are loads of revision websites and YouTube exam question practices they could do (if they're not going to get sucked into a google/YouTube hole and waste all their time)