The difference....

...that I've found between doing work experience in a school (and probably working there as a TA) and actually going into what you know will be 'your' classroom and 'your' kids is that I felt much more like I was meant to be telling the kids off and making decisions in 'my' classroom.
When doing work experience, especially since it was my son's school, I was very aware that, although they really appreciate my help, they were really doing me a favour by being there.
They all said 'ring me if you need anything' and 'don't hesitate to shout anytime next year if you need help' but still I was aware of not stepping on toes or doing anything wrong.
As soon as I went into the swap over day at 'my' school (that feels good, even just to think) I felt much more like the classroom was as much my responsibility as it was the normal teacher's.
It was good!
I also helped out at a sports day type thing and had responsibility for about 12 kids (with the school secretary) and I felt quite at ease both cheering them on, giving instructions and telling them off.
You do realise though -no matter how many of the school policies you read, it never quite covers all the little routines and 'hidden curriculum' type stuff that goes on. I found myself not knowing if the books go back in a particular order, or whether they keep used painting newspaper or chuck it away. It's silly stuff, but if you want to feel in control, you need to know the nuts and bolts. It made me look forward to having my own classroom (as NQT), although that seems such a very long way away!