The original IRTRAD discussion that Michael Robinson put on his website regarding the session history is at http://www.standingstones.com/session.html.

A more recent IRTRAD discussion focused more on the development in London after WWII
http://listserv.heanet.ie/cgi-bin/wa?A2=ind0207&L=irtrad-l&P=R16942&I=-3

I posed this question here because of a thread we are discussing on www.thesession.org titled "How long have "Irish" sessions existed in the US?"

As some people were relating early immigrants playing music to that being a "session",
my responses included the comment...could it be there was a conscious change in the development of what is called a "session" compared to people getting together in their homes to make
music? If the question is how long have small groups of people playing Irish music existed in the US, that is different than how long have Irish sessions (regular pub gatherings, not ceili bands) existed in the US.
The difference may be as simple as when people started using the term "session" and how the regular meeting in a pub was set up rather than playing at home or for a dance. There is also the diffenence that a session can be open to different musicians each time it meets.

To my mind, setting up a regular time for amateur players to meet in a pub rather than playing for dancers or at home is part of the "birth" of the Irish sessions. I'm just guessing. The recent IRTRAD discussion talked about how that happened among young Irish laborers in London in the 1940's. Anyone have info about the US development?