Science fiction & fantasy short stories suitable for English lessons

I spent the weekend with a friend who is an English teacher (that is, teaching literature to native English speakers, not teaching English as a second language), and in talking about texts, it emerged that their school doesn't really have much in the way of science fiction / speculative fiction / fantasy taught at any point, and they thought that it might be nice to study some for an upcoming short-story set of lessons, but they were not as conversant with those genres as with more traditional literature. So, I asked on Twitter (see first comment), and will ask again here, since I know any number of you are involved in SFF fandom, and because it makes a better repository for discussion:

What SFF short stories would you recommend for an English teacher to study with a class of 13-14-year-olds?