Even though the D.A. worked very well for some months, Marietta Edgecombe started doubting about this whole secret group and finally told Umbridge all about it. That same night, Dumbledore fooled Cornelius Fudge and told him that the secret organisation was his idea instead of Harry's, and fled the school. Umbridge replaced him as Hogwarts Headmistress (OP27).
The group used galleons enchanted with the Protean Charm to communicate to each other. When Harry needs help on monitoring Draco's attitudes as he and Dumbledore left the castle to find a Horcrux, the only members that answer when Hermione sends them a message are Luna Lovegood and Neville Longbottom. During Snape's regime, the D.A. members that were still at school reunited again. All the members of D.A. that were of age (as well as Ginny Weasley and Colin Creevey) fought in the final battle against Voldemort (DH30 - DH37). .
Some spells covered
In the meetings of the DA, they have covered the following spells:
Pages in category "Dumbledore's Army"
The following 28 pages are in this category, out of 28 total.