Yes, definately, when stonewalled it is appropriate to allude to litigation. Most people are self-serving and wouldn't want to justify their decision making in a court of law. I know I would give what you wanted if you put something in writing and sent it to me certified mail. It's a good thing you don't have my address. Who knows what you could squeeze out of me.

My kids go to a private school, but we looked into public schools last October when the private school wasn't working. The principals I contacted weren't interested in a grade skip (one said "Forget it" without even meeting my son). They gave me the "in-class differentiation" line and one told me they might be able to accomodate a one-year acceleration but "if you're talking about algebra in 2nd grade, forget it" (and my son started doing algebra in February of 2nd grade).