I've read a few things in MN recently which have made me wonder about this.
I work four days a week and over the past few years have volunteered in DC's classroom for one morning a week.
I enjoy doing this, but the my main motivation is to provide some genuine help to the teacher, in any way that suits them. My reasoning is that, the more help the teacher gets, the more time they have to concentrate on the core aspects of their job. I've done loads of different things, from listening to reading to sharpening pencils.
I was planning on volunteering again this year, but would hate to think I was actually more of a hinderance than a help........
I would be really grateful for any thoughts from teachers TAs.