claw, I think part of the difference is between state provision and private provision. I do not want this in any way to be taken as 'all private schools are better and all state schools are shite', but ime (dd1 is 7, and has been to a variety of placements, both private and state, ms and sn) the private school staff tendto be better trained, and, crucially, better supported.
I know the school 2shoes dd goes to, and it is amazing. my dd is at an amazing SN school (and was at ehr last placement too - also private). the staff I encounter are more than happy to have me as the expert on dd, and try to incorporate my knowledge into the day as far as possible. even tiny little things like knowng the home/school book actually gets read each day, and discussed (I had a tutor who had not been with dd1 that day come up to me to congratulate me about a success I had mentioned in her home/school book), and that each day I will be given both verbal and written (and truthful!) feedback on dd and what she has been up to.
I have 2 meetings a term, an hour long. the school office is alwyas open, or I can call them at any time. I get dd1's SALT reports, and the first page always says 'please read and call me if you have any queries', with a schedule of available times (3 days per week, a couple of hours per day); her SALT and OT attend each meeting too, as well as her head tutor and ABA consultant.
I am treated as an equal - I clearly do not know as much as them about the ins and outs of the school/daily life there/the curriculum, but they are happy to take on board suggestions for how to approach things, given my knowledge of dd1. there is no 'them and us' - it is all above board, transparent and all moving in the right direction. nobody takes a small criticism as a personal insult, but instead it is discussed, and a way forward hashed out. everyone is willing to (try to) see the others' position, and ponder over information in a new way.
I think all of this can happen at good state SN provision too, but that often it does not. same for ms - it is possible, but does not always happen. I also have to add that dd1 has attended a private SN provision where I was dismissed as delusional, staff ignored what I said about her and her needs leading to school refusal, and I was routinely told by the head not to tell ehr staff anything, as they did not have to listen to me.
I thnk, at the end of my ramble, it is about the leadrship of the school, and the teachers being secure in their knowledge. ime, teachers who are (genuinely) sure they are making a difference tend to be a lot less defensive than those who are trying their hardest to believe they are making a difference whether in ms or sn provision, state or private)
Folkgirl said it all better earlier, when she said that you need to know what you don't know before you even begin to learn about it. if a teacher is secure in what they know and do not know, and able to access support to learn what they need to know, then they are more amenable to treating parents as allies, not enemies.
just imo, though.