Seen a few over the years, was even one of each for older ages (one had mixed until about 10-11) active as I was growing up somewhat near to one of the houses I lived. You do also get a few, and several departments effectively that*, in universities (there was a women's college in the news the other month for telling their charges that your fertility drops like a stone after about 30, and possibly less than that, so consider that beforehand
https://www.theguardian.com/comment...ociety-fertility-seminars-barriers-parenthood ).
Originally there would have been an academic split -- make nice young ladies with requisite skills, diction and poise while making all the factory owners/lawyers/engineers/soldiers**/whatever out of the boys. I am sure I nice dose of puritanism did not hurt (might even have helped at some level -- boys and girls will be boys and girls... or indeed see "Mother and Baby Home"). Specialisation might be for insects but it has its perks on the economic side of things too.
*
https://external-content.duckduckgo...vel-and-gender-2013-2014-large.jpg&f=1&nofb=1 is older and less clear than it could be but illustrative.
** do remember most education is derived from military drills when that was discovered. One of the many reasons it is less than ideal today but I will spare that rant as I have done it before.
Speaking to those that went through it then it makes for some interesting dynamics, and not necessarily in the ways you would think (let's just say it predicts many of the same things that those times someone has the idea to run an all female company/department, albeit with the sociopathy of children and lack of hierarchy beyond simple social***). I don't know what goes in current space year though with internet and kids being allowed to roam around outside (though many of said same are probably lumped with extra curriculars and shut in the house such that they arrived at university with zero street smarts). I don't know what I can comment about academics for the ones I encountered as most of those would have been public schools (do note that public school in the UK is private school elsewhere, state school for the thing that government provides for all that need it. There are also private schools in the UK) and thus usually the kids of smart people (intelligence is quite a heritable trait) that went there so possibly skewed a bit, in addition to general funding boosts.
***technically you might have had head boy/head girl, prefects and age related fun with later years but... meh really.
https://thinkstudent.co.uk/what-is-a-school-prefect-and-what-do-they-do/ if you were curious.