The teachers seem to be free to do anything, short from killing someone. Well also THIS happens and Snape gets away with it but we can be explained with the political situation.
So the teachers may:
- Decide how to teach and what to teach in their classes. Examples:
- All DADA teachers had completely different style and content to teach
- Hagrid teaches whatever he finds interesting
- When Snape steps in for Luping as DADA teacher he just decides to start a lesson about werewolfes. While he does this out of malice, it again shows that the teacher do whatever he wants.
- Some teachers are more or less incompetent - Lockhart,Trelawney, Quirrell
- Award and take points from students on WHATEVER reason they find appropriate. Examples (there are lots of them but just giving the most extreme ones):
- Snape taking points from Hermione just because she wants to answer a question that he asked (first Potions class in Harry Potter and the Philosopher's Stone).
- Flitwick awarding points for very simple tasks in Harry Poter and the Order of the Phoenix (as a protest against Umbridge's rules)
- Snape taking points from Stebbins and Fawcett for (presumably) making out in the dark after the Jule Ball
- Give ANY form of detention to students. Usually the detention is not proportional to the violation done.The most extreme examples again:
- Sending Harry, Neville, Hermione and Malfoy in the forest during the night. Honestly that could be considered pure murder if something happened to them.
- Writing lines with their own blood (Umbridge to Harry)
- Answering fan letters (Lockhart to Harry). While not anything dangerous Lockhart is just using a kid to do his personal chores.
- Umbridge forbidding Harry, Fred and George to play quidditch (although she had special permissions in this case).