I think it will vary from between battalions and the PMS. When my older son went for his interview they asked ahead of time that at least one of us come with him. The APMS that did my son's interview had me come into her office with my son, she talked about the program and answered questions, I left the office so she could continue the interview. The PMS then asked me to his office, he explained the ROTC process in great detail and again answered questions, it was a great and informative meeting.
I'm sure every situation will be different, I would just be ready for however they decide to proceed.