Many independent prep schools will value your experience. What you need to know is that not all schools are the same and the variation in schools is huge compared to the state sector. I moved from a state middle school to a prep school in Sept, to a management position, so it is possible. Make sure in your application you sell what you can offer over and above teaching. In my application my ability to deal with data got me the job (IMHO) - it's much more a case of finding someone similar who can offer what the previous post holder did, e.g. did they coach the 1sts rugby team, if so they will need someone internally or externally to take that on, if no-one internally is suitable then this can be an important factor in decision making process when faced with two otherwise similar candidates. Good luck!