One of the sillier devices from the 1960s Batman TV show was the Batshield. This was a folding, bulletproof Lexan shield that somehow fit into Batman's belt:
Interestingly, a group of mechanical engineers at Brigham Young University have actually created a working bulletproof shield that folds. Using patterns from origami and 12 layers of Kevlar, here's what they came up with--and it's good enough to stop 9mm rounds as well as .44 and .357 slugs:
The unnamed shield is currently in the prototype stage, with the developers working with law enforcement to continue testing. Should it reach production, it's not difficult to imagine this being purchased, somewhat depressingly, by schools across America.