However, I'm confused now that you say "even if they're working and married". The rules are pretty clear about marriage. Support ends there.
Also - this answer suggests there's a possible change in circumstances, which is why I asked the question again:
BTW - I did read the Sandlin case and I believe the reason it did not fly was because the father disapproved of the girl living in a conjugal relationship, which did NOT fall under the rules of actually being married. Had the girl actually gotten married, the outcome would have been different.
For some reason, 'emancipation' with respect to self-support only counts for minors; not adult children (18-21) attending school.