I've been a LSA for the past 4 years after giving up a career in nursing. I've mainly worked in High Schools. I'm currently in a 1000 pupil school in a low-income area.
I follow a very varied timetable, including Home Economics, the usual academic subjects and a few sessions of woodwork and computing. I have identified pupils in every class, sometimes just 1 who has high needs, more often a handful who have a lower-level of support needs.
In reality, I spend most of my time dealing with poor behaviour. I tend to plonk myself in amongst the groups who are doing the most chatting, or I'll identify who is being the most disruptive, or winding up the noisiest pupil and I'll sit beside them and try to keep them on task - I'm a large lady so sometimes just being a visual block and physical presence can be useful. It's all firefighting, but I know the teachers appreciate that I can 'read' the class without them having to direct me since we only have 50 minutes or so to get through the lesson.
Do I get to the vulnerable pupils? No, not often enough, but if the teaching staff have to spend all their time dealing with the nonsense the vulnerable pupil isn't going to benefit anyway as the lesson isn't delivered.
I was in a lesson today taught by the Principal Teacher - he wasn't there when I arrived as he was needed in another class. I could hear the class from the far end of the corridor. When I arrived there were two boys lying on the floor in pain and several chairs scattered around while the rest of the class hooted and yelled. I had to shout very loudly to get their attention, something which I hate to do. When he returned he evicted four children and tried to start the lesson. He tried several times but we had to move two other pupils, one of them to sit beside me. I had to attend to the ejected pupils who were partying in the corridor. I never did get near the severely dyslexic pupil I was there to support.
I think the lesson began approximately 8 minutes before the end of the period and he got through one slide. He kept the whole class back after the bell to discuss their behaviour so they were all 10 minutes late for their next class.
I don't envy the teaching staff their jobs - I don't have to deal with the parents and I can go home at 3.30pm!