Training should be an ongoing event. Real world experiences change things every day. What is the accepted doctrine today may change tomorrow. A real training institution will recognize this and present a dynamic program with current information, and updated technique.
IMO a training session should be attended at least once a year. Training IMO should be well defined, organized, and unhurried. I dont think it should be limited to these sometimes expensive schools. A group of dedicated friends or shooters are just as capable of doing some research and come up with a training program and associated practice regimine just as good as any school.
Much of this opinion is based on the conversations, and posts I've read on this forum.