In Real Life, if a school is planning a major change of Dress Code, particularly if they're going all the way from "no shirt, no shoes, no service" to a strict uniform policy, they will announce it well in advance, seeking consultation from parents, teachers, the community at large if it's a public school, and often students, with any changes to take effect at the start of the following school year. (This applies to most other major policy changes, too. Schools are run by bureaucracies, and bureaucracy tends to move ponderously). Examples of Sudden School Uniform include: