I still think it can be done without dividing people. (I also feel that Archicad is not "that kind of program" that can easily be divided into "beginner", "intermediate" and "advanced" within a design & production environment.)
If the one-hour classes are modular (like, say, Solid Element Operations or Creating Viewsets), the topics could be something that a brand new user needs, but could also be something that someone with a few more years of architectural experience and spotty Archicad experience could still use.
I say this because I do the same thing: For a 50-person company, I teach a weekly 1-hour class and everyone from power users to new users to barely-CAD-literate project managers attend. It's been going for quite some time now (2 1/2 years), and almost never seems to run out of steam. People keep coming up with new topics, which are not always 100% CAD-related (like my current one on Work vs Progress
Average attendence is about 15 to 20 (there are 25 CAD users total), depending on some people being out at job sites, sick, on vacation, etc. Attendence is not compulsory, but both user ability level and amount of improvement are considerations for the staff at annual reviews. If someone is underperforming, their raise suffers. The easy way to fix that is to be in class.
Sometimes the rookies can benefit from seeing the power users in attendence (which says "Training is important for everyone"). It also means that the power users can contribute ideas and situations that the trainer may not think of, and the power users get reinforcement in areas they may not use often.
In my experience, dividing people makes them feel isolated or undervalued. Putting them into one large group and encouraging questions and participation made them feel like members of one big team that helps its own.