12yo 'keeps drifting off' during lessons-normal or something going on?

[Ashbeeee]

My DS, sweet boy, academic, has been top level for entire school career with seemingly no effort has suddenly had a downturn in performance. teachers saying he just drifts off in class, and he's just doing the bare minimum re classwork and homework. He's gone from top 2% in CATs tests to being moved down a set and getting low mark in all subjects - except maths. He's clearly upset by it, and I'm not sure how to help, or whether to leave him to work it out. We aren't the pushy 'you must be in top set' kind of parents but concerned that something's up.
Is it a phase? Is it teen onset ? I'm a bit puzzled. Any ideas , advice , reassurance most welcome. And I thought boys were simpler !

Not enough sleep?

Maybe he doesn't find the lessons engaging? I've seen what DS1's school typically do for lessons and I'd drift off. Its all powerpoint presentations - with the info presented in bullet points. Very superficial and I'd have thought quite boring over a prolonged period.

It obviously works well for most DC as the bullet points narrow down what they have to learn but I can easily imagine a more able student finding it engaging.

but I can easily imagine a more able student finding it unengaging.

Grrr! Autocorrect!

What does he say when you talk about it?

Well it's not lack of sleep as he's in bed by 9 and asleep (still asks to get tucked in) 10 minutes later. Bless.
Maybe he's just not interested enough. He says that some teachers are not interesting so maybe that's it? He does seem worried about his ability to keep track in class and worried that he's 'thick' vs his very clever mates.
Getting his eyes tested again as his glasses don't seem to be strong enough. And he gets a breakfast cooked for him every day so it's not lack of carbs either (in the morning anyway).
We do have some big emotional stuff going on at home with his grandad and great auntie. We are open about both situations but try not to expose too much to him as it's an ongoing situation with my dad and my Aunty is terminal, so there will be plenty of raw emotion once she dies, which sadly won't be long. . I think that he's probably burying some emotional stuff about that which isn't helping.
He seems a bit brighter today and got a good result in his geography test (unlike all of the others where he missed entire questions and only partially did the others). So some good and some bad.

Appreciate yr help Mners