This sounds awful and I’m sorry that things are so tough for you, balancing both caring and education for your DC.
I would say though that I really think it’s a fantasy to say that parents with time and opportunity can do anything to significantly change a school. I appreciate that it seems like that would be possible, but in reality parents have very little impact on the cultures of a school no matter how sharp their elbows. I was a governor of my DD’s primary school the whole time she was there, and it wasn’t even possible for the governors to do much to change the school culture, because so much of that is formed by intransigent things like the funding available, the SLT competence and style, the local authority/MAT dictating from above, the material buildings and fabric of the school, the availability of teachers and TAs. In some areas even if you have a TA-provision EHCP the school can’t recruit any TAs. Governors have a really limited purchase on the school culture if a controlling Head/SLT is determined to keep them out. Some areas are dominated by social problems that suck up the school’s funding and the SLT’s time to an extent that nothing else gets much of a look-in.
For the most part, helpful and committed parents are still just not going to impact on a school enough to make any real difference. Even less so in a secondary school — these are set up to have much less input from governors or PTA than primary, and your DC’s experience is much more dictated by the overall quality of teachers the school can recruit (and even governors will have very little ability to intervene in this as it is very determined by locality, funding and school culture).
In practice, the idea that parents can drive or affect the school culture in any significant way is more wishful thinking than anything else. Parents don’t create the school culture — the school culture attracts certain kinds of parents (and often the most middle class and financially successful parents are actually the ones who have the least involvement in the school - they choose a school precisely so they can sit back and not get involved. This is something the “middle class parents will drive up standards” argument never quite understands: the more well off the parents, the less time they generally have to contribute to the school — that’s often why they choose grammars or private to start with. Their kids going back into state isn’t going to mean they are suddenly in school lobbying for better teaching. The very opposite - they’ll just top up and tutor outside school time instead.)
I understand that this isn’t the reality people want to hear - it sounds like an ideal way to increase state standards is to say other parents are going to do it in some mystical way that doesn’t really cost any money but harnesses some magic class powers.
BUT, in reality what does it for a school is: a proper vision and leadership at all of the DfE/LEA/MAT levels, cold hard cash, good teaching, better facilities, a shit hot senior leadership team, decent classroom teachers and proper SEN provision and social support, and that’s expensive and lucky as well if a school has all those things in place. It requires a proper vision and strategy for education across the country, proper central funding, a local authority which knows what it’s doing, and a leadership team and teachers in a group of schools and the individual school who can put it all into action. That simply isn’t all going to happen just because Arabella and Sebastian who used to go to a prep and have middle-class parents have suddenly fetched up at the school.