In giving the actress the role of the teacher, the director was making a very specific reference to the 1983 film WarGames.
The quick appearance makes sense given that the blockbuster is set during the same decade when Sheedy rose to popularity on the big screen — but director Bryan Singer’s reasoning actually goes beyond that.
Those of you who were paying attention watching X-Men: Apocalypse probably noticed the special cameo early in the film, with Ally Sheedy playing Scott Summers’ teacher in the classroom scene right before the young kid’s mutation kicks in.