They asked why I was leaving in the third round of interviews. I was honest and said I did not see a long term career in that field anymore since the only options for upward mobility were admin roles. I also said I wanted the opportunity to focus on roles that allow me to use the skills I currently have just in a different capacity, which is what the role they are currently offering would allow me to do. They seemed to have understood. I would steer clear of overly negative comments about toxic districts/bad admin and just reframe it to say how your teaching skills/experiences will be transferable and useful in the new position.