For us it was also because the school and LA fucked up!
My ds is disabled and they'd refused an EHCP needs assessment.
Ds was being bullied and I'd tried to stop it and also get his needs met. His MH crashed and camhs referred his for cbt for school related anxiety.
Ds then had a knife pulled on him in class (2 weeks after a meeting that is called with HOY turned into 5 slt bullying me and suggesting I move ds if I don't trust them).
Ds was then too anxious to attend school.
His school refused to authorise an absence under illness for a pupil who threatened suicide graphically and was already under camhs.
I argued that he was entitled to a FT education under law and they had not met their legal requirement to provide a safe environment for him to learn that met the abilities and aptitudes of ds. Quite simply I told them the law and I would start judicial review/ legal proceedings if they didn't meet it. Eg 15 days after being too I'll to attend school they'd have to provide alternative education.
It's always helpful to email quoting laws and the UN convention for the rights of children and ask them how they are going to meet that.
Never ask if they can help. They'll them their duties and ask how they will meet them. Learn the law and use it. I use to ask how long it would take and when they emailed me with X time I'd email back asking for the new policy with X timescale and the one I had was the Y policy and Y timescale and I wanted to know my legal rights.
Obviously they were lying and it catches them lying and the more you can get them to lie thinking you know nothing the more they'll eventually do the right thing to rescue their own arses!
I think the best advice I can give is always do it by email. Be factual and bullet point. Minute any meetings and send to all attending.
And don't allow them to think you'll sit back and accept your child being bullied - let them know from the off you will be expecting a solution and there is no alternative for them to provide one.
Good luck 