<p>Just a quick little poll: did did your interviewers introduce themselves by their first names? I think some of mine did, but I tenes to err on the side of caution and addressed them by a Ms. or Mr. and their last name. </p>
<p>Some did, some didn’t. Andover was alumni, so it was first name, but almost every other school was by Mr/Mrs.</p>
<p>First Name/Last Name IIRC. I always respond Mr./Ms./Dr. with all adults, unless told otherwise</p>
<p>I grew up calling my friends’ parents by their first names, so with new friends, it feels unnatural to do it any other way. However, if I’m not sure, I’ll use a formal title. (Admittedly, though, I’ll often use my friend as a messenger. 
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<p>My daughters interviews had both: one introduces self as “Mrs. X” and the other as “first name, x”… We always defaulted to Mrs/Mr/Dr.</p>