Claire - sorry, missed that! Not sure what the source was, but the latest ISC report says that 73% of ISC boarding schools have less than 50% of pupils boarding, and only 3% are exclusively full boarding - and then some headline stats:
13% of pupils at ISC schools board. At sixth form this proportion more than doubles to over one third of all pupils. For junior pupils this proportion is significantly lower, with only 2% of pupils boarding.
In addition to boarding being far more prevalent at sixth form than at junior level, sixth form pupils are far more likely to board on a full-time basis: 91% of sixth form boarding pupils are full boarders, 6% are weekly boarders and 3% are exi boarders. In contrast, fewer than half of junior boarding pupils board full time"
So I think the two sets of figures do line up - which does make me wonder where all these FT boarding juniors are (unless they are mainly the older prep pupils in Y7 and Y8, where I accept there are a lot of FT boarders).
Maybe it's just because I'm in the SE, but I've probably visited about 20 boarding schools this year as we prepare for senior entry, and I've only come across about 1 or 2 where FT boarding (as opposed to flex or weekly) is the norm. It certainly looks from the ISC report as if there is a huge geo variation in boarding - some regions are as low as 5% of all pupils, with some over 20% (have excluded London for obvious reasons)
Boarding isn't for all children. My DD will weekly board in senior school, coming home every weekend. But she's built up to that through Flexi-boarding, which she loves. And we're choosing schools which are close enough that she can switch to being a Flexi or day pupil if weekly boarding doesn't suit. Just in case!