Hi All,
Do you know why they asked us about the other schools we apply for during the interview? Do you think it will be a problem if the applicant do not tell him all the schools he applies for?
There is no good reason to disclose that information and it is not required. It is perfectly appropriate to truthfully state that your child is considering schools that will challenge him/her in and that you are still formulating the list. It’s a polite evasion of an impolite request.
The Interviewer asked my son this question. He can’t say he does not know, because it’s now past the application deadline. I am not sure why they ask. The school even put that question in the application form
Is this a problem if my son did not tell him what school he applied for?
IMO, schools are trying to calculate their yield. For example they are trying to see if you are using their school as a safety. I agree with @ChoatieMom; I find the question impolite and have always evaded it. For my BS admissions process, my interviews were all well before the application date, so my answer was, “I’m still finalizing the list, but the schools to which I will apply offer X, Y, and Z.”
I’m currently going through this for college admissions, and my answer before the application deadline was as above. My answer after the application was submitted is, “I’m applying to schools that offer X, Y, and Z, such as AA, AB, and AC,” where two of the schools are at the same level as the school asking the question, and the third is a step below. I would not list all the schools, and I would list them in random (or alphabetical) order.
How I wanted to answer the question is: “I’m applying to all the HADES schools. While we’re on the subject of inappropriate questions, how much money do you make?” 
I think it is an especially inappropriate question to ask a vulnerable 13-year-old in isolation from any support structure (like a parent). Everyone gets the question. Some, like @skieurope, may be fast-thinking and mature enough at 13 to see it as improper AND to have a gracious response. Most will not.
I think it is asked to determine the level of school (Is their school a reach or at the same level? Is there a sibling at a rival school? Are they the only school being considered? etc.). An incomplete reply is not a mark against you. However an evasive demeanor or obvious attempt to be other-than-straightforward may be read by the interviewer as an integrity issue.
I agree with @skieurope. My son got asked this question at every school he interviewed at. He simply told the truth.
Just as long as the schools are in the same ‘range’, they won’t care too much. Schools are doing this to protect their yield. I suggest to be truthful, but simply answer with “I’m also applying to schools X Y and Z, which are very similar to yours”
Why is it an inappropriate question? I think it makes a lot of sense on the school’s part to ask, and if you don’t want to answer, pull evasive maneuvers. When I got asked that in an interview, I just said all of the schools (that I was applying to) that were considered “less prestigious”.