I went to a girls secondary school and vowed I would never inflict that on my daughter.
Well, fast-forward 30 years and I found myself enrolling my 11-year old in, yes, a girls' secondary (private, mildly selective which might be relevant).
She is very much a maths-and-science girl and we thought that this would be great for her, but to our surprise, the opposite was true. All of her friends seemed to endlessly complain that maths was hard and that science was boring. She was considered a bit weird for liking them and being good at them.
We moved her in Year 9 to a mixed school and she has thrived - finally she has mates who think that chemistry is cool, and who can match her at maths, and she is delighted. OK, it's mostly boys, but who cares, she's finally got some like-minded peers and that's all she cares about. She is one of only two girls in her computer science GCSE class, but at least they're running a computer science GCSE. In her old girls school, too few girls signed up and it got cancelled.
When we visited the mixed school, thinking about a move, I asked the (female) head of science how they dealt with boys dominating the class. She looked horrified and assured me that this simply would not be allowed to happen. I was doubtful, but everything I've now seen and heard confirms that she was right. Good teachers do not allow this to happen and will bend over backwards to support a girl who is into STEM.
I've recently discovered that DD has a 'boyfriend'. I think they very occasionally hold hands. I don't think there's been any snogging as far as my intel goes. I could not be more thrilled at this development. I didn't have my first boyfriend until I was at University and being at a girls school (and not part of the cool set that somehow knew boys) I had completely bypassed the snogging and giggling stage. At 18 it was straight into full blown adult relationship and I was Not Ready. DD will be, and I'm very pleased about that.