My school is very cautious in terms of violence, sex, drugs, alcohol, and any sort of expletives dominating the creative writing. That being said they don't restrict it from being included in the story; just be sure not to overwhelm your story with descriptive notions of how someone's being punched in the guts or something.
Be wary of the cliches, also. I know teachers constantly tell us to base our story from our own experiences (with that being said, as teenagers we really haven't experienced amazing adventures or far-away journeys, and thus stem our creativity from the ideas and concepts already present in texts). Try and think of something different, perhaps not the plot line; but maybe the context or even the perspective. Being a History student, most of my creative writing stories are set in some Ancient would (positive benefits for you, gives you an interesting plot and story and also reinforces your knowledge of History ~two birds one stone!).