It can be to keep people from just crossing that particular area. My school had a few fences like that, didn't actually fence the side area, it just ran along side of it, but the hobos, non-students, no longer had to just walk up access, actually had to walk around. From what I understand, it really did help keep them out, just because now it took extra work to walk the extra 50 ft.
It also prevented parents from clogging another area because now the kids couldn't wait in a certain spot for them to be picked up, and they all ended standing at the end instead, which was farther from the street light.