Your preparation and research is imperative to successfully answer this question. Provide a few reasons why you're interested in the school or district, and what in particular sparked your interest.

What is your personal experience with the school or district?

What do you know about its student body, faculty members, industry reputation, community involvement, educational goals and objectives, upcoming initiatives, demographics, or extracurricular activities?

This information will help you to accurately respond to the above question. The word accurate is important -- don't answer the questions by using old information

The interviewer is looking for evidence that you really know why you want to work there or did you just send out applications and hope for the best.

This research will also help immensely when answering other questions throughout the interview, so plan to dedicate some time and energy doing this homework. Effective research will help to tailor your answers, without being deceiving, to the question above.

It is wrong to tailor your answer with incorrect information - preparation and honesty is the key to a successful interview.