It's going to vary hugely depending on the affluence and aspirations of your pupils' families. It may also be affected by what else is on offer from the school: even in the most affluent areas, parents are unlikely to fork out for more than one residential a year, so if there are well-established trips in most year groups then you'll be competing with them.(On the other hand, if other trips are oversubscribed, that would bode well...) When I worked in a "poor" school, the ski-trip was only viable because it was open to all year groups, and went in termtime to get cheap rates. And it wasn't annual - some parents would only afford it once. Do you have a sixth-form and a decent cohort doing A-level? They may be considerably more interested as it might be useful UCAS form/interview material. Joint with other schools sounds like a good move, too.