And then there is me 
I asked a school to risk assess my son and I wrote to the governors to request that a behaviour management plan was put in place ASAP.
The SENCO laughed at me when I said the risk assessment was necessary... he had already kicked a teacher and was lashing out at children EVERY day at that point...
It was another 5 months of almost daily incidents before a risk assessment was put into place - 3 months after a group of professionals told them to.
Now he's in a school with a decent approach to discipline and his ASD... he was risk assessed before being allowed on school property.
Teacher training does not make you an expert on behaviour management - how much actual teaching hours do you get on that and additional needs during said training? Not much I am lead to believe...
And even if you have good personal classroom management the ethos of the school is vital to the discipline within it.
I would question if you have a) had much support from the school over these allegations from parents and b) critically reflected upon your own practice in order to identify areas that need change
Having a child with challenging behaviours is hard work at home, he's a friggin nightmare for teachers - some can manage him 90% of the time, others 10% of the time - often its approach that makes the difference however at the school I mention above - all of the teachers could only manage him for about 10% of the time because their support was non-existent...
His current school - most of the teachers can manage him 90% of the time and when it became apparently that staff were struggling in certain lessons senior management observed the lesson... some were merely time of day, change in teacher but with a couple of others... well he was moved out their lessons and educated elsewhere in the school. They are not bad teachers but their approach did not stand up to the challenging behaviour my son presents with yet I know that they have other 'tricky' children that they do very well with.
Telling a parent that if their child was better behaved then you wouldnt have to tell them off is not very professional... Much better to have told the parent the level of behaviour that is expected and explained how her DD did not meet that expectation, how it was dealt with in line with school policy and inviting her to discuss the ways in which you both could work together to prevent such a thing re-occuring...
Ofcourse they might just tell you to 'fuck off' but then that is whole different issue which then again needs to be dealt with at different level... kept seperate from the behaviour issues from the child and even if parents dont see the issue with their children's behaviour the school should have & follow robust procedures and exclude if necessary.
You see there is a tendency in schools to do something else - expect a type of behaviour from certain children according to their parents / circumstances... it's utterly infuriating when you are trying to teach a child best behaviour and they witness inequitable approaches...