I work in a mainstream school, which runs on a 6 period day. We have a small number of pupils who we (the team of about 7 TAs) support on a 1-1 basis in class, some with physical disabilities, some with learning or behavioural needs. In about half of our classes we are there for 'general support' in which case we are generally aware of a number of children in the class with learning issues (maybe Dyslexia or ADD) and we work with them, or sometimes we work with the noisy pupils which gives the teacher more opportunity to spend time with the rest of the class.
I enjoy it far more than working with younger pupils, the day goes by very quickly and you work within all the departments of the school and with most of the teachers. I also enjoy the intellectual challenge of jumping between 12yr olds learning German and 16yr olds learning Physics. Some TAs seem to prefer standing at the back of the class and only helping when they're asked to do a specific task, I much prefer getting stuck into helping with projects or working with a group - sometimes just sitting amongst some pupils and modelling the standard of work required is useful as it gives them a visual reference for what they're meant to be doing.
In creative classes I generally produce a piece of art or music alongside them and we can present it as a joint effort. I find this particularly useful for pupils with low self-esteem as often they don't begin a project independently as they feel as if they have failed at it already. In Maths/English I will circulate and support the teaching alongside the teacher, although I always refer to the teacher if I'm not sure I can answer the question, or help the child find the answer elsewhere.
What we (the TAs) don't have a big role in, is discipline. We will tell pupils when they have been rude to us or others, and we will talk to the teacher if it's serious enough but we don't have any form of sanction or penalty to apply. We tend to have a different relationship with many of the pupils and can be a bit less formal.
I was a trained Psychiatric Nurse and FE Lecturer before I had health problems and returned to working life in a p/t TA role. I only planned to be a TA for a year until I returned to my career, but 5 years on I still enjoy it even though the pay is poor. I think the children benefit from my support and I believe the teachers appreciate another mature, calm, well-educated body in the room. Best of all, when the bell rings I go home and take nothing work-related with me. That is very different from my previous careers.