As a teacher it's all too easy in a General forum, with separate groups, to post a message to "All participants" without meaning to. The result is that none of the students can reply.
If you are working with separate groups, having "All participants" pre-selected is not much help.
Wouldn't it be better for the drop-down menu to pre-select to an empty value, such as "Choose your group" (obligatory field), obliging the teacher to pay attention to this setting?
I've been caught out by this various times and I know I'm not the only one.
What do you think?