Harry Potter: Dumbledore's Army

When Professor Umbridge refused to allow her students to actually perform any magic but merely to read the theory behind it, Hermionecame up with the idea of asking Harry to teachDefence Against the Dark Arts to a group of willing students outside of class. He agreed somewhat reluctantly and the group held an initial meeting on October 5th at the Hog's Head tavern in Hogsmeade. After that, Dobby helpedHarry find a room called the Room of Requirement and the group began to hold regular training sessions. They decided to call themselves the "DA," which initially stood for Defence Association but which quickly was changed to Dumbledore's Army.

The members of the group signed a parchment which, unbeknownst to them, was jinxed. If any of them revealed what was happening, they would suffer a serious attack of pimples on their faces. In order to alert the members to an upcoming meeting, each person was given a fake Galleon. The serial numbers of the fake Galleon would change to show the date and time of the upcoming session and the Galleon would become warm.

Over the course of the year, the members of the DA learned a variety of spells, jinxes, and charms, including the simple ones like Expelliarmus, and some very difficult ones, like the Patronus Charm. Even Neville and the Creevey brothers became quite accomplished, thanks to patient, careful teaching by Harry.

Meetings ended in April when Marietta Edgecombe betrayed them to Umbridge and they were raided by Umbridge's Inquisitorial Squad. The discovery of the DA eventually led to the dismissal of Albus Dumbledore as Headmaster of Hogwarts (OP27).

In June, when several members of the DA accompanied Harry, Ron, and Hermione to London on thestrals to attempt to rescue Sirius Black, the found themselves engaged in a pitched battle with a group of Death Eaters in the Department of Mysteries. They fought bravely and well, suffering a number of injuries while defending Harry. None of the group was killed, thankfully, due to the timely arrival of members of the Order of the Phoenix.