When my kid saw their file, BOTH admissions officers said essentially, “Looks great, can’t wait to hear what the interviewer has to say.” One of the things that the interviewer told them was that the kid was not thrown off by unexpected questions. Well of course kid wasn’t! Kid had prepared by looking up everything kid could find about what Harvard wanted from the interviewer, including recommended questions. That is why, in this thread, I posted some links to articles about Harvard alumni interviews, and urged people to do their own research, too. The evidence in my kid’s case was that the interviewer’s feedback was extremely important.
Be prepared to talk about these things: What was most important to you in your high school experience - academically, socially, ECs. What Harvard might have to offer you, that other schools don’t. Why do you want to be there? What particular activities, majors, profs to study with, labs, anything you can focus on that says that your desire to attend Harvard is well thought out, not just a desire to attend a prestigious institution. Books you’ve recently read, what they meant to you, how you felt about them. What you do online - read the news? social media? engage with others across the world who share your precocious special interest in the resurrection of extinct Native American languages? Also, if you have particularly outstanding achievements, be ready to mention them, but in a tangential, non-bragging manner. My kid was too modest to do this, and apparently, neither the interviewer nor anyone on the admissions committee noticed these international level achievements. Still got in, but kid should have tangentially managed to bring these up in the interview, given the opportunity.
You might be asked what your worst experience was in high school. Personally, I think this is as rotten a question as the work interview question, “Tell me about your worst trait”. The right answer to that work interview question is, “My worst trait is that I am too conscientious, and I will work too hard to fulfill your expectations of me in the position.” I remember being asked this in my residency interview - I didn’t expect it. I told them the truth, that I had a bad sense of direction, and that it was probably going to take me a little bit longer to learn to find my way around the immense multi-hospital medical complex than others in the class. Harmless deficiency, not relevant to my work, easily corrected with a little time. In any event, if asked this, do NOT tell them about the bullying classmate or teacher, or the racist/anti-semitic/misogynist graffiti in the bathroom that the school did nothing about or {insert true terrible experience of your choice}. It’s a rotten question, shouldn’t be allowed. But if you’re asked this, you have to turn it around into something positive about you, and not something uncomfortable or awful about the school, or your experience there. "I think the worst thing that I encountered in high school was that I couldn’t find an outlet at school to continue my intense, unique interest in local political activity. The student council just didn’t seem relevant to the issues in my community at large. That’s why I sought out my State Congressional Rep’s office when I was in 9th grade, and have been working there and in my State Senator’s office ever since. I’ve had opportunities there that my high school just didn’t offer me blah blah blah. Turn the question into a positive, that allows you to share more about the reasons that Harvard should want you, and that you want Harvard. Be prepared, so you won’t be caught off guard.
Assuming you are offered one, the interview is apparently a very important component of the admissions process. Don’t go in blind.