CA schools started getting fences around them in the late '70s to the late '80s (bigger cities first, then spread to small cities). Has to do with liability when you hurt yourself on the slide, or whatever. Sheesk, I'm old enough to remember when school yards were just the defacto playgrounds of the neighborhood, after-school hours.
Not sure about Ok, but here in CA ...... at least in the cities around me, there is always usually still a turn-style opening, or a wide spot in the gate, where you can still go into the school yard. And of course there's always a sign with something to the effect "no trespassing, permission to pass revokable by owner, contact office to enter the grounds" or something to this effect. But people still just go right in, to jog the track, use basket-ball, etc... Ie.: the fences don't seem to have curbed the after-school usage. I think it's more so that if someone DID slip on a bananna peel, the school could still say "well you shouldn't have been there".
So we still hunt school yards here, despite fences (but perhaps some cities are buttoned up tighter, and it's actually enforced?)
