Good morning!
First of all I want to express that jillybean2's idea is great!
But I must admit that I am a bit scared because of:
Skill level: it depends on the context and the field you usually play in. I rated myself advanced, using the BBO definition. I would rate myself intermediate in a field of experts and beginner to idiot when I am tired. There is no definition what an intermediate+ / advanced player must know, some others mentioned that point earlier in this topic. On the way to become perfect I have the picture of a tree in mind. For the early basics you have the trunk, and with improvement the branches grow, one tree has many small branches 1m from the ground, another some bigger 1m from the ground and many smaller above 2,50m. What I want to say is that advanced player A must not necessarily have exactly the same knowledge as well as abilities as player B although they are both able to win even bigger tournaments.
The intention for visiting lectures for advanced has a very big variety: one player wants to practise on defence, one on counting, one on psychology at the table, one on squeezes, whatsoever. But this is easily solved by every participant himself who decides which lesson to join and which not, to stay or to leave.
Theory and practice: one might have read many, many books and know a lot about the theory of the game and therefore think that he/she is advanced or better (the books for intermediate/advanced players are already far too easy). All that does not necessarily imply that this person is an "advanced" player also at the table.
"Human nature":
a.) student: let's say you rate yourself advanced. You sit down at a practising table with 100 kibs. You start to play and make an error (or take a different line to what others think is correct) which is commentated immediately by the expert or at least 60 kibs. Isn't that mental stress for the players at the table? I've seen already many, many comments during vugraph or kibbing like "how did he/she get a star?" "Expert???" "And this person rates him-/herself advanced??" etc. Imo it is easier to "undress" oneself as beginner or intermediate.
b.) teacher: there is a nearly 100% guarantee that at least some of the visitors / students want to show the teacher that and where he errs and where the hammer hangs. It is a vision that people are just thankful for the service and listen and learn in modesty, taking what they need and declining silently what they don't. Look what happens to the most TDs who spend their time and knowledge for others.
I don't want to say that the idea is a dead born child, by no means!! I just want to express that all persons involved should carefully plan the format for the lessons to avoid disappointment. So this are my suggestions:
-The expert who offers a lesson should not allow everybody to talk at the table because that distracts the concentration for all. Perhaps a co-moderator, who collects and filters questions and decides which are interesting for the whole audience, would be an idea?
- The players who sit down to participate as students could get an anonymous nick like the vugraph operators. I don't know if that is possible by the software...?
- I personally like Mauro's idea of 4 experts playing and expressing their thoughts during bidding and play very much. My personal experience with watching vugraph is that seeing all 4 hands is not good for improvement. So perhaps the students kibitz only 1 expert who thinks aloud, experts rotate seats. That has the advantage that there is no overwhelming information by 4 persons at the same time, and 3 experts can rest

- I remember that I watched some time ago a lesson where someone prepared hands for a specific topic. It worked like Fred's learning programs. Great, but A LOT of work for the teacher.
Have a nice day, folks
Caren
Those are my principles. If you don't like them I have others. (Groucho Marx)