Looking of chat sites for training

I am looking for chat rooms that students can use without having to register or download software.
I want them to just enter a name and password and start chatting. Can anyone advise me of any such sites.
If not, does anyone know of chat sites that students can register with minimal fuss. Some of these students have not used the internet before, some are older students. I want to keep it very simple for them, otherwise they may be frighten off.