Yesterday brought up 2 other issues to consider when using Yahoo!Groups in class: firewalls and web-access.
Everyone signed up (or I signed them up) ok. They got their welcome message from Yahoo!Groups and the one from me. But nothing after that. Messages they send to the group get stopped by the firewall. Everyone got a message titled (in English) Barracuda Spam Firewall, but the content was all garbage characters, completely illegible.
I asked about this today and was told that students need to add the yahoo group to their white list. How do they do that? "They'll get a message from Barracuda. The instructions are all in there."
"Erm, I think they already got that message."
The other issue is web-access to the group's messages. To ensure maximum privacy, I had switched this option off when creating the group. Now that no-one in the group was getting each other's messages, at least until we learned how to add the group to our white list, perhaps we could at least read the messages via the web. Perusing the group settings, I couldn't find a way to change this setting (this in Yahoo!Japan).
I also, belatedly, realized that signing students up directly means students do not get a Yahoo!Japan ID (unless they happen to have one already). If they had one, they could sign in to the group and read and send messages that way.