<p>I don’t know anything about art schools, but having been involved in accreditation processes of colleges under a different body, I can share what I know. </p>
<p>It’s usually a matter of a school meeting or not meeting some hard specific criteria (e.g. X hours offered in X courses, number of faculty who are X, criteria for admissions is X, resources available to students include X, % of X, and ratio of X) and/or a school not bothering to become accredited (not enough gain for the hassle). </p>
<p>Usually you can find the required criteria by the accreditation body (e.g. google NASAD), and can see where a school deviates. That often explains it. </p>
<p>But from my experience, school reputation far outweights accreditation, making it less valuable (if not unvaluable) to those already established. Thus it helps the no-name schools (usually when people boast that their school is accredited, its because no one has ever heard of it), but does little for a school already well established and recognized in their field.</p>