In the education field, motivation is an important factor for interviewers. They will want to understand what is attractive for you about this job. Steer clear of focusing on summer vacations and other perks of working at a school. Be prepared to talk about what you hope to get out of the job, in terms of helping students to be successful and happy. This question really lends itself well to examples from your own life. Whether you had a guidance counselor who really excelled or one who failed you, undoubtedly your experience working with them will have led in some way to your choice to enter this field. You may want to explain why you want to work in education, and then expand into why you chose counseling over teaching or a similar area.