Just came across this thread and very interested as it is one of my real hobbyhorses! As someone who has been playing in Irish sessions for some 30 years on a variety of instruments I cannot abide "elitism" in sessions. The truth is that nearly every time I play I learn something new, often from so-called "inexperienced" players. In seventeen years playing in one well-known session in London I never saw one person turned away, asked to leave or criticised. On the other hand, I have sometimes been cold-shouldered by "insiders" in new sessions I have been to and it doesn't feel good and certainly makes me even more sensitive to the feelings of learners. Basically it all boils down respect for others and good manners. These days, if I detect "elitism" in a session I don't bother going back.

mcmoo