This is one of the few openings to really focus the interviewer's attention on your finest qualities. Take this opportunity to explain why you are the most qualified and most passionate about the job. Your specific and genuine answer here could really set you apart from other candidates, so be sure to think about your response ahead of time. It's important to research the school's values and mission before the interview. Choose a skill of yours that you think is aligned with the values and mission, and connect it with an innate character trait.
For instance, if a school is known for being strict due to rowdy students, you may want to highlight that you're very good at classroom management. Or, if a school is known for a strong liberal arts program, you may want to highlight that you're very creative.

If you know the school lacks a particular program or in an area you feel strong in, be sure to communicate your commitment and ability to lead in that area. Schools are constantly on the lookout for dedicated teachers who will be assets and strong leaders within the building; share your ability to do just that.