Have the students bring in something by their favorite writer and analyze the style of a passage of it? I dunno, when I was in high school I vaguely remember having an assignment to imitate two of the writers we read for class that year, I picked Poe and Hawthorne (almost the same style, really). Other people picked Dickens or Hemingway. That year was all classics though, so there wasn't anything more wild to pick from like horror, postmodernism, surrealism, science fiction or fantasy. Given a free choice I probably would have picked C.J. Cherryh, C.S. Friedman, Paul Park, or William Golding.
When I've given personal mentoring to a young teenage writer I usually find that they are interested in learning terminology - what kind of viewpoints are there, what is a character arc, what is freytag's pyramid, what are genres, etc.