Dumbledore's Army

Also known as the D.A., Dumbledore's Army was an organisation created by Harry Potter, Hermione Granger and Ron Weasley in their fifth year at Hogwarts, intended to teach other students at the school how to defend themselves against the Dark Arts. This secret society became necessary when it was clear that Dolores Umbridge, the fifth year Defence Against the Dark Arts teacher, would not properly teach them anything. The group met in the Room of Requirement and used enchanted coins to communicate with its members. Harry taught the group some of the basics of duelling, such as the Disarming Charm and Impediment Jinx, as well as advanced magic such as the Patronus Charm.