My take is that many schools began offering neuropsychology concentrations once students began showing more interest in the area, which probably related to talking with psychologists who were/became interested in the area, who themselves became interested after hearing neuropsychologists made more money (at that time) than non-neuro psychologists. Thus, at least to me, it's often (although not always) felt primarily like a marketing move.
I've heard of the programs but don't have much direct experience with any of them. Like WisNeuro mentioned, your best bet is going to be identifying programs with faculty who are neuropsychologists (and, for programs with the traditional mentorship model, applying to them/their labs for admission), that offer classes in neuropsychology, and that have neuropsychology practica available.
Having an explicit concentration is not at all necessary for boarding. The above factors (i.e., neuropsychology coursework, mentorship, practica) are much more important. Although even then, there are folks who have limited neuropsychology training in graduate school, but who are able to make up for that on internship and fellowship and attain board certification. However, I think someone who received essentially no training in neuropsychology in graduate school would be pretty hard pressed to fill in those knowledge/training gaps, in part because they aren't going to be as competitive for the types of internship and fellowship they would need.
