I'm looking for a copy of this short story for a teacher in the elementary school where I'm media specialist. I've found a copy on the web, but I need to direct her to a hard copy. Was it published outside Fantasy and Science Fiction magazine? Thanks for any help.

All Summer in a Day was published in:

Twice 22, A Medicine For Melancholy, and The Stories of Ray Bradbury. I know it was also (and probably still is) published in several literature anthologies for secondary school use.

I'm aware of these. It is a much-anthologized story.