Totally agree with tech/a.
Another No-No I found out (the hard way): Don't try to "educate everyone to get everyone on the same level". That won't lead to "constructive discussions", but more likely to your pupils trying to second-guess what you may think about a stock. Almost like you talking to yourself.
Forums aside, where everybody comes with a different background, education, mindset..., I have been involved with two trading groups:
1. In the time after attending a popular and intensive Training Course, a group of like-minded people decided to stick around and meet weekly at first, fortnightly later to discuss ideas, methods, technical interpretations. In between meetings, we stayed in touch by email and in a casual chat room.
2. The chat room, set up to accept members only, gradually replaced/ made unnecessary the meetings in person. It also led to like-minded traders from Interstate being invited to join. At its heyday, we had about 20 members, not all of whom would be online all the time. The GFC caused more than half to drop out, most of the leavers gave up trading altogether and decided to "live off the proceeds". Meanwhile, we're down to a hardcore of 4-5 regulars, who share watchlists, opinions, and alerts - even though each of us may trade different time frames and even instruments - from small-caps to blue chips to long and short MINIs ...
PS: Wysiwyg makes also a valid point about group members losing out. Most people will happily continue to apply what they have learned and understand. If conditions change and their "method" turns from money-spinner to money-pit, many will give up, rather than go through another round of education/ adjustment. More often than not, well-intentioned suggestions that they should adjust - even giving concrete pointers where I thought they were stuck in a rut - has broken friendships.