You should do it at your old primary school. I know it doesn't may not sound like the greatest place, but I know i definitely enjoyed it more and got a lot more out of it than my friends who did theirs with lawyer firms and the likes.
I did my work ex there, (yes, admittedly because it was the only thing I could get at the time because I'd decided to leave it until last minute), and at first I really wasn't looking forward to it, and I just wanted it to be over already, but after the first day I wanted another week there.