I always say if it matters to you ask never assume. I have a friend who sent her not overly bright but talented golf mad DS to a well known boarding school and then moaned about the lack of golf course she just assumed there would be one.
It also never ceased to amaze me how frankly daft some parents are they seemed to assume that as they were paying they will be free to do whatever they like. At the "new boys lunch" in the term before DS2 went to his well known senior school I listened to three parents say how they were disappointed to be told that their DS couldn't either weekly board or be a day pupil! The school clearly states on its website that its full boarding only, at open days it states its full boarding only and one even already had a DS there who full boarded! Another moaned about the lack of single rooms, despite admitting to having had two tours of the boarding house!
You are paying a considerable sum of money don't just go round a school and take everything you're told as gospel, ask difficult questions, never forget that the vast majority of boarding schools are struggling to fill their vacancies despite what they'll tell you, they want your money. A few years ago a bursar at a very big name boarding school who had just returned from some sort of bursars conference told me that only about 8 or 9 boarding schools had more really suitable applicants than places and that they were basically the very very big names usually the super selectives, most were struggling to fill all their vacancies.
Also if you're looking for full boarding there are only a handful of proper full coed boarding only schools left.
The sort of question you ask should be about things that matter to you and your DD personally, for example if youre abroad and think that you might want to bring your DD home a day early because that works well for flights ask if this is possible, as its sixth form do check that the school offers the subjects your DD wants to do and she's able to combination she wants. A while ago a mum on here moaned that my DS's school didn't offer business studies drama and other perhaps slightly easier and less academic subjects in the 6th form, this is a school that prides itself on intellectual academia above everything else. Again the subjects it offers are clearly written on their website. If you and your DD love what I consider to be ridiculous outdated uniform or like me dislike uniform try and find a school that matches your views ditto with things like meaningless ritual. DS's school didn't want parents to be over involved that suits me as I don't want to be over involved, another friend loved the fact that she could log on and read her DS's grades very three weeks, hopeless for me I struggled to logon once a term to read a report. DS's prep ran various concerts pays etc and we were told although attendance was optional, but in reality it was actually compulsory especially things like nine lessons and carol concerts (wince) etc. I positively loath this sort of thing it was such a relief when he went to his senior school and there was hardly any of this stuff to attend, but you might feel differently.
I always advise people when looking around a school to quote Kenneth Clarke although in a different context to look look and look again. Try and see a school on a normal day not on an open day, watch what's going on, watch staff with pupils, the relationships between staff and pupils will be less formal, watch the pupils going about their day to lives they should be more relaxed than in day school remember you are in their home, talk to as many pupils as you can, not the buffed and polished ones giving you a guided tour, the normal ones, do you. like them? On one visit to DS's school I sat with a group of lower 6th boys whilst they ate their lunch, they were some would say shockingly honest, in particular in their outspoken views of their HM, 8 years later I heard DS2 say the same things at the same stage in his education about him, but on leaving he had nothing but praise for the man what a year ago seemed irritating at then end seemed reasonable and most importantly caring. My DS reminds so much of one young man I talked too, I can see that on first meeting he was not everyone's cup of tea, allowed to be totally eccentric and outspoken, his intellectual curiosity and interest was what I hoped to see in my DS at that age and also the freedom to not conform and Im delighted to report that is exactly what has happened. DS2's school was hopelessly slack liberal that suits me I'm hopelessly slack liberal. But you might not want this thats fine were all different thats what makes us so interesting. Try and find a school who's ethos chimes strongly with your own.
Its not easy most schools are not only very clever marketing machines but also becoming increasingly homogenised, many have hideous videos with bright eyed polished and bushy tailed children saying no school has better teaching facilities opportunities than there's earnest heads saying how special St Blogs is, how they will bring out the best on your DC with muzak being played in the background. I've worked in a few, had friends with DS's at most of the well known ones, mums love to compare notes when they meet for this ghastly mothers lunches lunch after all what else is there not talk about? A few exceptions aside IME the wrapping might be different but underneath most broadly offer pretty much the same stuff it's the title details that are different.