I read all Malory Towers and St Clares as a child, and a fair few secret sevens and famous fives, some of the Naughtiest Girls and some of the real drivel like the faraway tree stuff.
I always felt EB was more 'committed' to MT than StC's in a way - I think she enjoyed writing Darrell much more than those twins (and who would have guessed that PAT would be the sensible one and Isobel a bit fey.....)
I remember reading Trebizon and finding it a bit lame, but getting through anyway because I was one of those girls who just liked school stories! I do remember how she always used to refer to 'the Greek girl' and 'the black girl' in them though. Seem to remember the black girl was a super runner.....
I think writing a new boarding school series, although it would be fun, would be too difficult now because of class and so on. Even Ann Digby obviously felt that Rebecca had to be at Trebizon for expediency (father working abroad for seven years and company pays the fees), rather than just being wealthy and posh (as Tish was).
I'd find it fun to write one but I'd really struggle not to start putting things in about how invidious private education is all the time, and not make the girls a load of stuck up prats!
Does anyone remember Jean Ure's 'Peters' series? I think she was trying something similar (early 90s), with a Nicola Marlow-like heroine, but in a very unlikely sounding single sex girls comp in London, with blazers and summer dresses and people having crushes on the netball captains....