It doesn't sound like there has been an imaging done. If that's the case I would be asking for xrays and an MRI with dye.
I would also make sure that the kid knew that for now head-first sliding is an absolute no-no for him. Lots of shoulder injuries come from that, not to mention fingers, wrists, and necks, and from what I have been told a loose shoulder or a shoulder that has already dislocated is more likely than others to do it again.