Here are a couple of suggestions about things you really ought to avoid on that occasion.
1. Do not be late.
It is such a simple thing, but being late for the admissions interview suggests that you are inconsiderate and discourteous. Many private school admissions offices have back to back interviews scheduled at busy times of the year. If you are going to be late, call the office and advise them as soon as you realize it. Offer to reschedule the interview. When you finally arrive, apologize for being late. Then don't draw any further attention to it.
2. Do not tell them that their school is not your first choice.
The admissions staff know that you are looking at several schools. No matter where their school may be on your list, be cordial and non-committal. The purpose of the visit and interview is for you and the school to scope each other out. You are trying to determine if this is the right school for your child. They are doing the same thing. But coming right out and telling the admissions staff that their school is really not the one you want is just silly. Who knows? Perhaps the school you really want will turn your child down. Never burn your bridges.
3. Do not come across as a difficult, demanding parent.
Educating your child is a partnership of three: the school, the parent and the child. Ask pointed questions about the school if you must. But don't be abrasive. (Incidentally, a good educational consultant can ask those pointed questions for you and allow you to keep your distance.) No matter how terrible the day has turned out before you reach the admissions office, put on your best face and be the epitome of graciousness. It also never hurts to let the school know that you are willing to help out when asked.
4. Do not try to impress them with your money and social position.
You may be worth billions. Your ancestors may have come over on the Mayflower. But the reality is that schools champion diversity these days. They are proactively going after students who ordinarily could never afford a private school education by offering completely free educations. Many schools can afford to pass you over simply because they have huge endowment funds. They prefer to admit the most qualified candidates regardless of their financial and social circumstances. Diversity rules. Get used to it.
Be humble. Leave the car and driver at home for another occasion. Dress neatly but modestly. A Talbot's dress or Brooks' Brothers suit as opposed to the Dior or Brioni outfits will speak volumes for your humility. For some reason the school will probably know how much money you have anyway.
5. Do not be overly familiar.
The interview may have gone very well. It may indeed be obvious that they like you and your child. But don't get carried away. Be gracious, not effusive, in your comments. It would be inappropriate to suggest that the admissions staffer have lunch sometime or give her a hug. A smile and a polite handshake is all that is necessary.
Remember: the interview part of the admissions process needs to be handled adroitly. Both you and your child are being examined and assessed in more ways than one.
Finally, don't forget to handwrite and snail mail a thank you note to the admissions staffer who met with you. This old-fashioned social touch is much appreciated in private school admissions circles.