The meeting broke up with the agreement that sessions were to begin once a suitable location in which to train had been found. Umbridge used the information to implement Educational Decree Number Twenty-Four, which banned all student organisations that were not approved of by the High Inquisitor. Initially, Ron thought that a student at the meeting had betrayed them, until Hermione pointed out that if they had, she would have known about it due to the jinx she placed on the parchment that they all signed.
Although not revealed at that time, Aberforth Dumbledore also relayed information about the D. Despite the ban, Harry assured all the members that the meetings would go ahead once an ideal location was found. Soon, Harry was informed the Room of Requirement by the house-elf Dobby, who occasionally used it to store the drunken house-elf Winky. During the first session, Cho Chang created the name Defence Association, but Ginny Weasley suggested to make the letters DA stand for a different name of their group, Dumbledore's Army, to frighten the Ministry officials, since they were frightened that Dumbledore was creating an army to take over the Ministry;.
Hermione arranged a meeting in the Hog's Head during the first Hogsmeade visit of the school year for anyone who wanted to learn, although Harry was sceptical that anyone would turn up.
After Dobby told how to summon the Room to Harry, Hermione, and Ron, the D. Harry started them off slowly, practising the Disarming Charm (Expelliarmus).
When Zacharias Smith scoffed at its simplicity and wondered about its effectiveness, Harry responded that it was the spell that saved him from Lord Voldemort in the Little Hangleton graveyard.
They claimed that Cedric Diggory's death was a "tragic accident", and refused to admit that Voldemort had murdered him.
Concerned that they needed defensive magical skills to combat Lord Voldemort and his Death Eaters, Hermione proposed the formation of a practical study group to be taught by Harry as he had more experience than any of them with using actual defensive and offensive magic following his encounters with Lord Voldemort.