Hmm, wondering if the 'answer' lies in a combination of these. A Happy hour launch event for staff from the school (or district if going large) with snacks etc and "Failure Facilitators" to get the discussions going in an informal manner. Then have sign up sheets towards the end of the event for people who would like to join up with a smaller, more personal Fail Club for the year.
What a great failure - a failure due to unexpected popularity. To me, this shows how powerful this idea could be. Perhaps, this informal happy hour is a great prototype for a launch event or for where smaller fail clubs could meet a couple of times a year. That way there is a social element added in, but the focus for most of the year is in smaller groups so discussions can be facilitated more effectively?
It would be great to get some feedback from all those who were there: was this what you expected? would you like to be part of a smaller fail club in future? etc.