Is it necessary to wear a suit to a Private Girls School job interview?

Remember that, in America at least, any Tuxedo rental place will also rent you a suit. It may be worthwhile to rent a suit rather then buy one just for a single interview.

Can you at least get a blazer, if not an actual suit? My company is very casual, but I've still heard prospective candidates get dinged if they show up to an interview without a suit. It comes across as a lack of effort to some people, I think: "jeez, guy couldn't even be bothered to dress up a little..." I think this is a fairly common reaction anyplace where wearing one would be the norm, unless you planned on explaining yourself.

I used to work at the world's most casual private girls' school imaginable -- in California, of course. Uniforms were logo t-shirts on top, any color; bottoms were free choice and ranged from tutus to pjs; teachers generally showed up in t-shirts and jeans. Board meetings featured pizza and most of the board wore jeans too. Anomalously, a candidate for Head did show up in a suit once. The kids (who were conducting many of the interviews) repeatedly reassured her "It's all right, this is <name of school>. You don't have to dress up here!" She insisted that it was all right, she liked suits. The kids were incredulous, but they liked her. So did almost everyone else. We hired her. Moral of the story: it can't hurt. (I didn't wear a suit to my interview, but I did dig up a jacket.)

As an ex private school girl... yeah. Unless that school is so far north you're in the Torres Strait, wear a suit. Even if you don't suit up once you've landed the job, it won't hurt to err on the side of dressing a bit more formally/professionally. Can you maybe go to a mens hire shop? I think even a blazer would be see you through. However! If you don the great Aussie male school teacher uniform of knee-socks, sandals and neatly pressed shorts set off with a tidy short sleeved shirt... I will hire you myself. Your colourways are blue or brown. Super bonus spiffy points if you pull off a combover. Sir!

Well that settles it...managed to pick up a great suit and it looks much more professional.

This is one of those (often unfair) situations where if you and some other candidate are equally matched with qualifications and charm, they are consciously or subconsciously going to choose the guy who dressed up and wore the suit. I've seen it happen.

Suit up or don't even bother going to the interview. Even if you are north of the tropic of capricorn, wear a suit. Maybe, just maybe, if the school is on TI itself, you might get away with a shirt and tie. If you can't buy one, hire one from a formal shop for the day.

Suit or you don't get the job. I favour the 2nd hand clothes shops in the bohemian parts of town for this (i.e. Newtown in sydney, not sure where in the other capital cities)

nth suit.