Interesting comments.

As an AF/NAVY fobbit kind of guy, the model I've seen work best is a kind of hybrid - on PT days (which were 3 days a week), the unit would muster in the morning at the Gym. Everyone would sign in for accountability purposes and then individuals would PT on their own. Once every two weeks, usually a Friday, we do some kind of group PT, usually a run or a mock PT test. Anyone who failed the yearly PT test got supervised PT every morning and then retested in a month. I thought that system worked pretty well and provided a decent balance.