Garrett-ace350, turn your question around the other way, and ask yourself: Why wouldn't it be allowed ? For example, do others go there after school hours to jog the track, shoot hoops, etc.... ? If so, would think to yourself : "I wonder if I can fly frisbees there?" (afterall, you might poke someone's eye out).
Odds are, any question like this, would not be about md'ing in-particular (I highly doubt there's anything specific in school yard codes about that anywhere). Instead it would revolve around persons at all being there after school for any purpose. And I'm sure if you asked long enough and hard enough, you'd always find someone to say "no". But as you can see, there is usually no shortage of someone walking their dog, shooting hoops, etc.... An exception might be if you're in an area where the schools are truly buttoned up with fences that have utterly no entrance.
And dain-brammage: I've gone back to the link again, and there's a whopping 1 or 2 cities there. Just a few that have happened to dream up something when it came across their desk as a "pressing issue that needed answering". It doesn't list "all cities".