“The Ministry’s forced through another decree, which means we’re not allowed to have Quidditch teams —” -- Harry Potter (OP17)
The Educational Decrees were co-created by the Hogwarts High Inquisitor, Dolores Umbridge, and the Ministry of Magic during Harry’s fifth year at Hogwarts. These rules were set by the Ministry of Magic in order to assume more control over Hogwarts. The Ministry also desired to change the standards of the school through censorship, especially involving the return of Lord Voldemort.
List of Educational Decrees and their statements:
22: "in the event of the current Headmaster being unable to provide a candidate for a teaching post, the Ministry should select an appropriate person." (30th August) (OP15)
23: "which create the new position of Hogwarts High Inquisitor." (OP15)
24: "No student organisations, societies, teams, groups and clubs may exist without the knowledge and approval of the high Inquisitor." (OP17)
25: "the High Inquisitor will henecforth have supreme authority over all punishments, sanctions and removal of privileges pertaining to students of Hogwarts, and the power to alter such punishments, sanctions and removals of privileges as may have been ordered by other staff members." (OP19)
26: "Teachers are hereby banned from giving students any information that is not strictly related to the subjects they are paid to teach." (OP25)
27: "Any student found in possession of the magazine The Quibbler will be expelled." (OP26)
28: "Dolores Jane Umbridge (High Inquisitor) has replaced Albus Dumbledore as Head of Hogwarts School of Witchcraft and Wizardry." (OP28)
29: "if I (Filch) could've strung you up by the ankles in my office, would they? But when Educational Decree number 29 comes in, Potter, I'll be allowed to do them things..." (OP28)
The Educational Decrees are featured in Harry Potter and the Order of the Phoenix, though they are mentioned once in Harry Potter and the Deathly Hallows when Snape reinstates an old decree: “Snape had reinstated Umbridge’s old decree forbidding gatherings of three or more students or any unofficial student societies.” (DH16)
Veritaserum is connected to the Educational Decrees. Dolores Umbridge, after catching people violating the Educational Decrees or for other disciplinary measures, used Veritaserum on students. This is illegal, though she never actually uses it. She had Snape make this potion, but he gave her a fake potion.