Look, chaps.
Start by re-reading the thread title:
Triple Science MISTAKE. At the time of DS's options, a decision was taken based on a) his interests, b) his aptitudes, c) his abilities. Whilst a young NQT teacher who had known DS for all of 6 weeks thought he should go into a 'top' double award class for GCSE, the highly experienced Head of Science (note, not Head of Year in this instance) whom we met with personally; me, DH and DS, agreed that on balance DS would be able to achieve well in Triple Science. I should add, for fairness- though maybe I don't need to as half of you seem to be following me closely thus can probably quote me!- that I discovered between DS being suggested double and us seeing the HoS, that the school don't offer normal paced triple. Which would have been ideal for DS. But he wanted to do Triple, the HoS who is in charge of a very successful Science GCSE programme at the school, felt he was able, though cautioning there'd be no swapping to double. So, I think I can fairly say that it wasn't necessarily my mistake, we went to the experts and sought advice. I don't think it was the school's mistake, as such either. DS was achieving well in science and meeting all his quite high targets and wants/wanted to do 'science' as a career but is weaker and less interested in Biology, and here the HoS agreed with us; that a poorer performance in biology double science would bring his overall mark down; doing less well in stand-along Biology still left Physics and Chemistry safely 'ring-fenced'. As it is he'll need 'B's for the A levels he wants to take -anyone here like to start quoting me what grades their local 6th form require to prove I must be lying?... currently though although he'll very likely pass his triple subjects, he may well not get that B. All his exams are to be taken at the end of Y11 to whoever asked.
So, anyway, he was put in a Triple class. Which he's struggling to keep up in due to the sheer volume of work and having to cover stuff at home that he could use the teacher's input into.
I'm sure Talkin can fill you all in on this via asking her DD's 14 year old friends who are actually at the school in question, via FB, how it all works. Though why those 14 year olds can be relied upon to know whereas mine can't eludes me. You have always come across as a bit of an expert about this school despite having no DC there, and a family member who drops in a couple of times a year. TBH, I do sense some jealously from time to time even though your DC are at a nearby, excellent school ('gerrymandered catchments...').
How did it go.. 'End of'?
Yes, a year ago when GCSE decisions were made DS, like an awful lot of 13 year old boys, wasn't seeing 'the big picture' about his education. Do people really think that we should have made him choose the soft, easy options at GCSE just in case he never matured enough to knuckle down of his own accord? I guess some do: I recall talking on here about DS's needing help to get stuck in with homework and revision and being soundly told that I was wrong and that I wouldn't be there to chide him onwards at university thus shouldn't, now ... 
But we are where we are, now.
DH and I went in and saw the HoY last week due to a lacklustre report (where the info about self-teaching came from, the HoY, not DS) so we are 'talking to the school'! Some general strategies have been put in place but any work DS was planning on doing over these hols has been 'back-burnered' by his impending (Y10) Business/IT GCSE.
Telling me how your school does it, unexpected, is all very interesting but does not constitute help or advice, does it?
Coconutty- you may be confusing me with someone else: DS always wanted Triple, it was a NQT who suggested DS (and several others now also in Triple) did Double. But sadly, and oddly, tutors seem to be in short supply around here!
Sashh -I can only tell you what the HoS told me: that 'dropping back' wasn't an option beyond the first 6 weeks as the syllabi diverged, or maybe 'the way it's taught' diverges. As it is, his timetable says 'Science', not P1, C2, B1, P3 etc.
I genuinely want to thank all those who have offered practical suggestions, support and solutions to this dilemma; but yes, I am defensive because I have effectively been attacked and gloatingly mocked by several on here who are delighted that my son is struggling as it will serve me right for being so full of myself that I overrode everyone to insist DS did Triple, against all advice.
Which is not the case at all.
But again, thanks for the support and useful suggestions.