very often people say that applications/ interviews shows if person would fit in... how would you interpret it? Is it possible to "learn " it to show that you will fit in, or persuade that you would fit in?
I interpret it as skills set and personality that match or enhance the existing team. Is it a school where team planning happens? If so, is there evidence of you being a team player. Or, is it a school where the working environment requires more independence and initiative? We have had candidates arrive who clearly clash with other staff - too assertive, know-it-all, think they are god's gift, and others who seem to express in interview they want to work in a multi-entry primary school as others will have done / will do all the work.
I think you can learn to show you will fit in by thinking about how you interact with the school staff outside the interview room; being friendly and interested in what others are doing, without being ott; maybe mirror a bit of body language; mention your adaptable approach, flexibility; research as much as you can about the school and really reflect that in your application form and discussions.
However, if you are not a good fit, do you really want to present yourself as something you are not - would you really be happy working there?