Am surprised at the boys school comments as girls sport seems to be more dominant. As a boarding school it is open 24/7, with staff living on site, which gives it quite a buzz. Very much work hard, play hard during termtime This week on top of "usual" weekly clubs and practices, there is House Art, House drama, Junior Spelling Bee, a brass competition, Book week (including a photography competition), CCF bushcraft day, an army field day and the Boarders talent Show as well as auditions for next term's Shakespeare play. Plus midweek and weekend sports fixtures including a swimming gala against RGS.
Holidays are bliss - no work (though I suspect it will not be the case at 6th form!).
Setting seems to mainly happen from year 9. Top sets do very well indeed, children in middle sets get mainly As and A*s. Where it falls in league tables seems entirely dependent on how many lower ability children are admitted each year, but the lower sets are full of happy busy pupils who don't seem too stressed. The school allows internal candidates with B grades through to 6th form where, once they are doing their 3 or 4 preferred subjects, they seem to shine. This is possibly the key difference against other local schools who have stricter criteria. But Caterham seems to treat the pupils as individuals not a herd, and is looking for pupils to be successful longterm, knowing that progress isn't always in a straight line. They do reward both effort and attainment.
Don't think it is particularly harder or easier than other local schools at 11+. Maths paper is 7-8 problems to solve (no easy warm up questions), English is straightforward, and reasoning is time-pressured.
Don't know anything about Prior's Field but they're getting a gem of a head teacher (from a parent's perspective).
But as all threads on all schools end up: do take travel into account! We're local so it is a no brainer.