Thanks for the further feedback and haven't had time to come back on and reply to everyone!
Have now emailed the HOY to query a homework audit carried out last year and explained DS's current difficulties and will see where that gets me.
Should just re-emphasise that DCs LOVE their school and would really, really hate to leave at this stage. I've already spoken to them about the financial situation and suggested the possibility of the local state 6th form college (which is excellent). So far, both are very keen to remain at their current school.
I presume that if there were just a little easing off of homework demands, plus an improvement in his processing and concentration, then DS would feel happier. I think it's just the sheer relentlessness of each week, having to get up early, do a long day, come home and work again and then get maybe 30 mins before bedtime to do anything other than HW - that's making DS feel fed up.
Teenage hormones must also be contributing to his feelings too, I suppose and then of course my own busy life, exemplifying the treadmill of work.
Because of how hard the DCs work at school and on HW, I'm always reluctant to make them help more domestically.
Other children do plenty of outside activities - like sport etc - but we can't afford anything that costs more money and there really isn't time for me to take them to things at weekends, unless it's a quick drop off at school for a one off activity, as I work on Saturdays. Because I work in the evenings, I can't pick them up from school later in the evening anyway. But they already feel there's too much on and prefer some downtime - if they can only get it.
Thinking about some of DS's peers, there are those (lots of girls and some of the very bright boys) who have excellent organisational skills, plus a huge aptitude for subjects that are very factually based - eg Maths, Physics, Chemistry, Biology etc. So for them, they'll just get down to work efficiently, find the content of the work easy (and some of these children work ahead of the cohort anyway) and whisk through any homework, leaving time to practice musical instruments, do sports etc etc.
Other peers struggle more than DS or have a more slapdash attitude towards work than he does. The former spend even longer that DS on homework and are adversely affected by greater processing issues or perfectionistic and obsessive tendencies. The latter dash off any HW at odd times - like on the way home or at break - don't care how they do but are bright enough to remain in the school.
DS is sort of in the middle, in terms of ability, has slight - but not horrendous - processing difficulties and sometimes perseverates on work and sometimes dashes it off. I think the school is a good fit for him and the main thing is that he's happy there and wouldn't want to leave.
I think we'd all prefer if though if there were much less HW and then only specific work that is going to be useful for progress - not work for work's sake (think drawing cartoons of a Shakespearean play or theatre, designing posters for History etc etc - which he occasionally gets and feels to me like a waste of time, as he'll take hours over this!)