Once you're hired as a teacher, you won't be wearing a suit to the classroom. Smart, but relaxed attire is more appropriate to the busy, hands-on atmosphere of school. But your initial interview is another matter. You always want to appear reliable, professional and trustworthy -- you can achieve that look with a suit.
The standard advice for interviewing is to dress one step more formally than you would in the role you're seeking. That advice works well in a teaching job. It's likely that the administrators interviewing you -- the principal and either superintendent or assistant superintendent will be wearing suits. You may feel awkward being more dressed down than they are. Dress to impress.
Stick with a conservative grey or dark blue suit, but you can wear either a skirt or pantsuit. A pantsuit gives an air of practicality, which is no bad image in a teaching job. With your well-cut suit, you can also have a little pop of color with a nice scarf or a patterned blouse. This can give an impression of an outgoing personality, which is also an asset in a teaching job.
Accessories and Grooming
You will need to carry your resume, teaching portfolio and lesson plan examples. Invest in a slimline leather portfolio to gather these together for your interview. Your hair should be recently cut and styled. If you have long hair, consider wearing it back or up. Your makeup should be minimal and professional-looking. Don't wear large or clunky jewelry that will be distracting.
You do have options if you don't own a suit or can't afford one, or don't feel you could relax wearing a suit. A smart knee-length or mid-calf skirt with a silk or cotton blouse also gives a professional look. You could also wear a tailored dress with a structured jacket.