One of mine is at a well known boarding school right at the top of the fee scale, OP (scholarship and bursary). I earn well below the average UK salary. The admissions process is essentially 'needs blind'; a third of pupils there have some kind of fee assistance. The pupils don't know who falls into this category (unless they choose to tell other pupils). In truth, though, they don't care.
For every pupil who goes on the ski trip/safari trip/whatever, there are 10 pupils who don't. Nobody knows why or cares why some go and others don't (though, FWIW, at this particular school, trips are discounted by the same percentage as the fees, for pupils who qualify for fee assistance) - precisely because they don't want trips to be open only to the better-off pupils.
All the pupils seem pretty confident they are there because they have something great to offer (music, sport, academics, art - anything at all: the school encourages excellence in any sphere, however oddball it might seem); their backgrounds and their parents' earnings are irrelevant because they know one another mostly in the context of school, where everyone is treated equally. As a result, there is a better social mix at that school than at my other children's day schools. At these latter schools, it's always the 'rich ones' who go on trips, have expensive clothes etc. Though they are a minority, as most people have nothing left for extras once they have paid school fees.