DS15, Y10 grades are slipping, how can I help him

[AllInTentsWithPorpoises]

DS15 is generally a good kid, he is well liked by his teachers. He is very like me in a lot of ways and having a problem focusing/ carrying out tasks in full is one of those. He is not what I would call particularly academic, more creative. He has pretty average-ish grades, is predicted around 4/5/6 in most subjects. But he is slipping in these grades (we've just had a report plus his most recent exam results). He has help with his basic english language skills 2 sessions a weeks but when I caught up with the teacher recently she told me he'd missed some sessions and been late to the rest. He seems to be getting more unmotivated recently.
I want to help him keep on track or improve where he can without smothering him as we have a pretty good relationship. His dad veers from not being involved to being overly involved with little middle ground, he only sees the kids every other weekend despite living just a mile or so away.
How can I help him? Do I need to ask him to look at what he is handing in for homework? How often is that realisitically feasible because I know if I do that every night it will drive him nuts. He struggles with pressure and I just want him to not keep sliding.
Teens are hard, even if they are lovely.

Just to add, we've spoken about the langlish language help and I will be much more on top of him for getting there on time plus we are looking at a maths tutor. I'm just finding it hard and I'm worried about him.

Sounds like he needs some incentives? Is there spare money to put towards something he wants if he attends the sessions and gets his grades back in track?

Help him do a study time table.

Have you excluded learning difficulties?

Bribery!
What does motivate him?
I'd sit him down and point out there's only this year and next and the exams are done. Keeping on top of work now will make next year easier.
How is homework set? I would say a nudge at the weekend to make sure he's done any outstanding homework ready for a new week.
Is a tutor outside of school an option to help him with tricky subjects? Catch up classes in school might be embarrassing him.
Make sure he has a decent space to study and keep track of when he has tests etc. When he gets a decent grade in something make a fuss - get a takeaway, let him choose - basically reward the effort so there's a reward for at least trying. Be positive, realistic but don't chivvy him all the time.

I have wondered if he is on the threshold of having inattentive ADD. He is a terrible sleeper, has trouble organising himself, loses stuff and forgets stuff regularly and daydreams a lot. I approached it with his school who assessed and said they thought he wasn't but are now giving him 2 sessions a week to help with focus concentrating on his english language skills primarily. I've been told it can be really expensive to get him assessed privately and I can't afford it. So currently I need to manage it as best I can.

Such a difficult age and with the added pressures of GCSEs the poor kids can feel overwhelmed.
Firstly they have half term coming up, I would let him have the week off other than an hour or so sorting out a homework or revision timetable.
secondly- ask him if he is worried, sometimes the grades are based on the latest test results and the test may have been in a topic he found more difficult than previously.
Thirdly, lots of encouragement, praise and rewards for progress! Remember when he was a toddler and the big achievements mattered? It’s the same now! He needs to hear it just as much as when he was 2!

When are screens going away at bedtime? Our DS used to be on them very late which knocked on to everything else.

I'm trying all of this. I mist have said there is only this year and by next summer it's done a million times. Maybe the bribery would work, will have athink about what to bribe with!

The book Smart but Scattered might help - I found the first sections useful in pinning down my ds' (and my own!) strengths and weaknesses - like you, I think my ds is borderline ADD but the book defines it in terms of executive skills which I find helped focus me on where he needed support. The book is included in Audible if that's useful to you.

Thats a great recommendation for the book, I'll have a look tonight for it

I think that the advice to treat him as if he has executive skills issues isn't a bad one. Talk to him about how he thinks he can most effectively study.
Teens definitely respond better to rewards than sanctions.
Rewards don't have to be expensive. It's more about thought and showing him you are proud of his achievements (and helping him to value the positive consequences of getting a bit of work done).
Regarding sleep - my DD had been a poor sleeper in that she found dropping off really hard, her mind was too busy, the thing that seems to have helped the most has been a weighted blanket.

he has a weighted blanket and it has helped but it means he's gone from really terrible to slightly terrible - so great but still a bit of an issue.

I really like the idea about executive skills - its really positive which could be a really good thing for him.

Has he ever been assessed for dyslexia? This often goes hand in hand with executive skills deficit/ADHD. The school may be able to screen and assessment is much cheaper than ADHD (about £500 round here).

OP school aren’t qualified to assess whether he has ADHD, particularly inattentive type. ADHD is effectively executive function skills deficits. Perhaps you could approach the school senco to see if they would support you in requesting a referral for NHS assessment? This won’t cost the school anything.

Just to add, I've just seen this on my podcast recommendations and it seemed relevant to your OP Google Podcast link