Dumbledore's Army, also known as the D.A. or Defence Association, was a secret organisation initiated by Harry Potter, Hermione Granger, and Ron Weasley to teach their fellow Hogwarts students proper Defence Against the Dark Arts in 1995. This organisation was made necessary by the refusal of Dolores Umbridge, the subject's professor during the 1995–1996 school year, to teach anything in her classes other than textbook theory. It had approximately 28 members. The group was disbanded during the 1996–1997 school year following the appointment of Severus Snape as Defense Against the Dark Arts teacher, although several members heeded the call and participated in the Battle of the Astronomy Tower at the end of the year.