A common trope used to give a character or characters a chance to interact with old classmates and/or as a flash-back to the days when they were in school. Sometimes used to portray how much a character has changed, grown-up, or become "cool" (or alternatively, how the character hasn't changed a bit), or just as an excuse to put the character in a funny looking wig, glasses or braces.
Often, the [...] [tvtropes.org]