High school graduation is an impressive milestone for a teenager to achieve. And considering how most parents feel like it was only yesterday that their graduate was starting kindergarten, the end of a teen’s high school career can also feel pretty emotional. So cue the waterworks, because there’s a social media trend that's really driving home the imagery of how quickly kids grow up. High school graduates around the country have been returning to their elementary schools in caps and gowns to wave to current grammar school students and say thank you to their former teachers. Called a “senior clap...