As a teacher, this is how I see it.
I work in a secondary school in a deprived area. We have a wide range of students from different backgrounds.
We have a specific email every week about students that have 'special considerations' due to additional needs. Many of these students, we are told, cannot be sanctioned for not following the rules e.g. talking, missed homework. We are meant to refer to Learning Support, but nothing is done, so the child receives no consequences.
The British education system is rubbish. We teach students to pass exams and there is no fun in learning - so much of my subject is interesting, but it's not on the curriculum/exam spec, so I can't teach it.
As for students who have 'unmet/unnoticed needs' - if they are violent and affecting the majority of the class, they have to go. It's unfair on the other students who are in the room, and the staff member who is trying to deal with the issues. It doesn't help that parents don't parent their child - I had a parent ask me to tell their daughter to go to bed at a reasonable time because she had tried and her daughter had 'been nasty' to her!
You then have the parents who always believe their child over you as a professional. 9 times out of 10, SLT bow to the parent for an easy life (for them). It then makes the teacher's life difficult as they have been undermined for the rest of that child's academic career.
Just my thoughts, as someone in the sector.