The short answer: a private school interview typically runs twenty to forty-five minutes, scaling with age: twenty-odd minutes is the common middle school length, with upper school and boarding conversations running longer. The parent conversation is usually around twenty minutes, often in parallel. Lower school "interviews" are play-based visits on their own clock. And one rule before any of the numbers: the length of your child's interview tells you nothing about how it went.
The bands, by age and school type. Drafted to field norms, and every school will tell you its own format if you ask. Middle school, day school: twenty-odd minutes with one adult, while parents have their own roughly twenty-minute conversation nearby. Upper school: usually longer, thirty to forty-five minutes, with more weight on the student's own voice. Boarding schools: the interview itself often sits at the longer end, inside a much bigger visit: tour, sometimes a coach or teacher conversation, occasionally more than one interview across the day. Lower school: not really an interview at all, a play-based visit with its own rhythm, covered fully in its own piece. Zoom: same conversation, similar or slightly shorter length, same listening.
What fills the time is the same arc at every length, and knowing it is the real preparation: a warm-up the interviewer runs on purpose (previews, easy openers from the child's own world), the middle conversation (the question pool this site decodes), and the child's turn. "what's a question you have for me?" A longer interview isn't more questions fired faster; it's the same arc with more room, which generally favors the slow-to-warm kid. Time is runway, and runway is a quiet child's friend.
Now the tea-leaves paragraph, because every family reads the clock and the clock lies in both directions. A short interview is usually a schedule, not a verdict. Admissions days are stacked, and twenty good minutes is a complete conversation. A long interview is often a talkative kid or an unhurried afternoon, not a signal of special interest. Interviewers themselves don't treat length as data, and the write-up doesn't record it. Whatever you do with the drive home, don't spend it doing arithmetic on minutes.
The practical uses of knowing the length are the honest ones. It powers the preview, which lowers anxiety more than any other single fact: "about twenty minutes, shorter than a class period, then we get lunch." It shapes the day's logistics. You can plan the arrival margin and the after-food around a known window. And it right-sizes the event in the family's mind: this is a conversation the length of lunch, not a tribunal, and families who hold it at that size send in calmer kids.
One last format note so no version surprises you: some schools fold the interview into a larger visit morning (tour first, conversation after. A sequence that quietly favors slow-to-warm kids), some run parent and child conversations simultaneously, a few do everything on one revisit-style day. None of the variations change what's being listened for. Ask each school what the day includes, write it down, and hand your child the preview. The formats differ; the four things never do.
Jennifer Hines spent twenty years as a Dean of Admission at Noble and Greenough School. Her free guide, What They're Really Asking, decodes fifteen interview questions from the other side of the table, and shows why the quiet kid is often the one who lands them best.