There are several novels that might fit this description. In such a story, the contrast between the gangster's rough past and the innocent high - school setting can create a lot of drama. Maybe the gangster has to deal with things like school rules, making friends in a new way, and facing academic challenges that are completely different from his gangster life.
I'm not sure which specific novel you're referring to. There could be many novels with such a plot. It might be interesting to explore how the gangster adapts to the high - school environment, whether he tries to leave his past life behind or if his old ways cause trouble in the school.
Well, without more details, it's hard to give a precise account of the novel. However, generally in a story where a gangster becomes a high - schooler, there could be themes of redemption. The gangster might start off with a bad attitude but gradually change through his experiences in high school. He could encounter kind teachers or classmates who influence him positively, and there might be conflicts with his former gangster associates who try to draw him back into that life.