I was interviewed by an independent school and told they would phone and let me know, but probably not that evening. I received a letter telling me I had been successful a week after the interview - and two days after I had seen the position readvertised. I was not impressed. Personally I think it's good manners for a school to phone and let you know either way, as you took the time to come and visit them for an interview. Some schools do but I don't think it's unusual for rejections to come through the post.