You know all those super adorable, OMG! How Precious!, my baby is such a genius pieces of art that you bring home from daycare, then throw in a box to eventually "organize and preserve"? Yeah, you should totally write the date on the back of those construction paper masterpieces. Otherwise you'll be faced with some hard decisions later down the road. Like making up dates.
Also, I've decided that preschool teachers WAY overuse the glue-and-tissue-paper medium.