At lunchtime I run a voluntary class on Barthes' essay The Death of the Author. The room is packed - students plus one of my colleagues. We get through a couple of paragraphs & then broaden out the discussion to connect to the current course.
The atmosphere is relaxed but completely focused. All the more remarkable given that a) by any standards, the material is challenging for a group of 16/17 year olds; b) they're giving up their own time. & it's evident that everyone is getting something out of the 45 minutes (me included). At the end there's a general agreement to pick up where we left off next week. I find I go into the next 'official' class with renewed enthusiasm.
Such occasions are enormously rewarding & need in some way to be 'bottled' against all those times when - for one reason or other - you wonder whether it is worth it.