Learning Disabled Students , referring to some of those in Special education.
LSD, where the D and S are intentionally reversed. This originates from a line by Captain Kirk from the fourth Star Trekmovie, The Voyage Home. In it he mistakenly calls LSD by LDS in order to explain Spock's unusual seeming activities (by saying that he used it) to a 20th century human. One of the funnier moments in the movie.