Thanks Birdman. Glad your son's situation ended well. We're dealing with only one pars, but it is a complete fracture (it was clearly visible on the x-ray). They also did an MRI to check for any other concerns. They did not find any. I suspect the combination of pitching, hitting, and weight training all contributed to the initial discomfort and the eventual fracture. It is possible he has actually been dealing with this for over a year but, until the bone completely fractured, he was able to work through it.
Fortunately, our instincts about the first ortho doctor got us to a much better doc (pediatric and sports med) so I'll echo your suggestion (and those from your other links) about finding the right doc. First doctor did not even suggest a brace until we asked for it and only limited physical activities to things that did not cause pain. Not good protocol for an active 16 year old boy.
It has been 4 weeks and he's wearing the brace 23 hrs a day. Yes, it does need frequent washing! Physical activities are limited to walking and a recumbent bike at the YMCA. We also purchase a CMF device (electromagnetic therapy) that he uses for 30 minutes a day. The better doc used this for his son (also had a pars fracture). Doc felt the CMF device improved the healing process and likely shortened the recovery period by 2-3 weeks for his son (took 16 weeks to "return to sport"). My son goes back for a follow-up next week. Sure hoping for some good news, but realize it is still early in this process.
Thanks again for the reply, info, and advice.