I've taken pictures at soccer games. Regularly end up with ~100 "share worthy" pictures. I upload them to my Google Photos account, put them in an album, then share a link to the album.
If you're talking about pictures taken during class, I'd check with your principal on what you're allowed to share before posting. You can't count on parents not sharing links, and some parents don't want images of their kids online.
I figure when I've done soccer/softball/basketball/HS Graduation pictures, all participants are in the public eye, so no expectation of privacy. School classrooms I would think would be different.
