Yes, we have done a few of these and they are very easy to prepare for.
The meeting will probably be with the headmaster, a deputy head or the head of admissions, who will undoubtedly be well aware that your DS or DD is petrified by probably their first ever interview and will do everything they can to make it as easy as possible.
Their main concern is that you aren't sending someone to boarding who doesn't want to go. The questions we had were mostly to put your DS or DD at ease, like:
- What are your favourite lessons at school?
- What are your favourite hobblies?
- Are there any subjects you don't like?
- Tell me about a book you read recently.
- Tell me about your family / siblings / pets.
- What do you know about our school?
A couple of schools also asked our DD why she picked that school, at which point I interrupted and said we had chosen then school after talking to our daughter about what she would like in a school, and pointed out a couple of good things (great reputation, great facilities, lots of boarders.....), but it is also good if your DS or DD is prepared to say something about the school - whether it is great at sports, or drama or whatever. Everybody thinks their own school is great so you can probably say anything complementary and they will believe you.
They will also ask if they have any experience of boarding, know people who board or if they have been on any residential trips where they were away from home for a few days, and how they felt being away from their family.
Then they will explain that everybody has good days and bad days, and will ask your DS or DD how they think they will handle it they have a falling out with one of their friends or if they get stuck on their prep (homework) or if they miss their parents. One school asked if there was ever a time our DD felt sad and how she handled it, who helped her.
They basically want to hear that your DS or DD understands this and that they know to speak to the housemaster or matron about personal issues, or their tutor about academics, or will ask to phone home (though they would probably prefer it if your DS or DD says they will speak to school people about their problems first before phoning you). What they don't want is someone who is going to hide everything and then start self harming in their dorm.
Overall I think if your DS or DD comes over as reasonably confident and doesn't look scared of boarding, you'll be fine.
There is always the obligatory "do you have questions for us?" Or DD always asked how many people slept in a dorm and something about sports teams. Then I asked about how boarders and day pupils mixed or did they keep to themselves, and then about the activities for boarders at weekends. It's like a job interview. You have to look interested, but if you've done your research you probably know the answers.
Remember, so long as they have room a non-selective state school cannot reject you because they don't want you at the school. They will only say no if they think boarding will not work for your DC.
One of the schools asked to interview my DD alone, but I just stood off camera. The others were all happy for me to be there.
If anything else comes to mind I'll add it later.
Good luck and don't be nervous. Let us know how you get on.