Re: broken clavicle redux
Anecdotally, shoulder separations are pretty common (and more common than clavicle breaks) among beginners learning forward rolls.
This seems to be mostly from either 1. launching or 2. not maintaining arm extension.
Some dojo teach beginners to roll by having the shoulder firmly on the mat, in order to avoid this.
There is still a risk that in transitioning to regular rolls folks will "launch" onto the shoulder.