I think that part of the problem is that we have so many separate unions (Okay..."Professional Associations") that refuse to work together.
I'm trying not to out myself here. I mentioned a violent pupil above...
The reason that we were landed with this little darling was as follows. (I only got the info about the previous school second-hand. The info about our school is first-hand knowledge.)
One parent worked in a solicitor's office and threatened to sue the council if the whole school transfer was not to a school of the parent's choice.
Why were we chosen? The parent had, I was informed by an even older member of staff, been a problem pupil at our school. As best as we could understand, said parent had a grudge against a particular member of staff and was determined to...Lord knows what.
The pupil had been violent at their previous school, a member of staff had intervened and the parent had (predictably) claimed that their child had been assaulted by the member of staff.
Teachers in Scotland are - we were constantly told - not allowed to refuse to teach specific pupils. However...
One of the union reps at the previous school called a meeting for all teaching staff and pupils support assistants. This is highly unusual.
They persuaded all those present to refuse to interact with the violent pupil. That's as much as I know, but it was enough to force the SLT, LA and parent to agree to move the pupil on...to us.
I haven't given the full story here, since I don't want to out myself (as I've said). I will say that I'm now fully retired and no longer on the GTCS register.
So you're right. The problem is that we [former in my case] teachers rarely seem to be able to work together.
I've been in the EIS and I've been in the SSTA. In the highly unlikely event of my re-registering as a teacher, I'd join the NAS/UWT - their reps seem to have more balls than anyone else, largely because of better backing from their head office.