Passage: The Simpsons uses a floating timeline in which the characters do not age or age very little, and as such, the show is always assumed to be set in the current year. In several episodes, events have been linked to specific times, though sometimes this timeline has been contradicted in subsequent episodes. Bart's year of birth was stated in "I Married Marge" (season three, 1991) as being in the early 1980s. In "Simpsorama" (season 26, 2014) Bart states his birthday as February 23. He lived with his parents in the Lower East Side of Springfield until the Simpsons bought their first house. When Lisa was born, Bart was at first jealous of the attention she received, but he soon warmed to her when he discovered that "Bart" was her first word. Bart's first day of school was in the early 1990s. His initial enthusiasm was crushed by an uncaring teacher and Marge became worried that something was truly wrong with Bart. One day during recess, Bart met Milhouse and started entertaining him and other students with various gestures and rude words. Principal Skinner told him "you've just started school, and the path you choose now may be the one you follow for the rest of your life! Now, what do you say?" In his moment of truth, Bart responded, "eat my shorts". The episode "That '90s Show" (season nineteen, 2008) contradicted much of the backstory's time frame; for example, it was revealed that Homer and Marge were childless in the early 1990s.Bart's hobbies include skateboarding, watching television (especially The Krusty the Clown Show which includes The Itchy & Scratchy Show), reading comic books (especially Radioactive Man), playing video games and generally causing mischief. His favorite movies are Jaws and the Star Wars Trilogy. For the duration of the series, Bart has attended Springfield Elementary School and has been in Edna Krabappel's fourth grade class. While he is too young to hold a full-time job, he has had occasional part-time jobs. He works as a bartender at Fat Tony's social club in "Bart the Murderer"...

Question: What grade did Edna teach?
fourth