as a general rule yes...most classes are kind of done on a points system...you earn points towards your grade for a total that is equiv to an A/4.0.
and yes, the students can only see their own grade info
one professor I had, had an extra credit section that included links related to the general class and you basically had to comment on it for like...10 points (overall class points were 1500)
class discussion is very interesting if you're dicussing something like lit, or sociology..but I don't know how that would translate to something like SCUBA
its generally not moderated but I would imagine for kids you'd have to keep an eye on it