I agree that most parents don't know the half of what goes on in schools, and I think teaching is often a thankless task. I also don't expect teachers to be perfect, and accept they make mistakes, cos they're human, just like the rest of us.
I understand that teachers have a class of 30, whereas my only concerns are for my three little darlings. I have, in fact, had massive support from one particular teacher.
I have almost always supported their school/teachers even when I've disagreed with them privately, and accept that my children may lie, although DS3 is renowned for being brutally honest, often to his own detriment.
I do know however that one of their teachers has lied to me in the past, amongst other suspect behaviour.
I am also conscious that I failed to follow up a situation with a member of staff when DS1 first started secondary. I put the ongoing situation down to "clash of personalities" "getting used to new school/new rules" etc etc. I then met a woman who knew this teacher from 20+ years before and her instant reaction made me think that I maybe should have intervened. When we next met with the Head of Year, I mentioned his slide in this subject, and although the HOY was very professional, unfortunately her face also told me that this teacher had unfortunately not been so professional.
That is two members of staff I've come across in 10 years of education, so very minor in percentage terms, but the point I'm trying to make is that sometimes parents do need to intervene on their child's behalf.