Perhaps your father-in-law remembers a time when "making prom" was synonymous with "getting promoted." I'm pretty sure that "prom" is derived from "promotion." I'm "only" 64, but there was a time, before the libs foisted "social promotion" upon us, that the issue of whether you were going from fifth grade to sixth (for example) or repeating fifth, was not fully resolved until you received your report card.
yeah, but still in this context, she wouldn’t know if she wasn’t being promoted til mid_june. and yes i remember that too, there were kids who were worried they wouldn’t pass. back in the days when we were 64 kids to a classroom with a single nun at the front, who would clap her hands to tell you to shut up, and you had to stand up every time an adult came into the classroom. looked foolish for several weeks when i went to public jr high and had to break that habit of standing for adults.