The new principal of one of

the state's largest (and most expensive) private ("public" to readers in the UK) co-ed schools made some very public remarks about single sex education causing emotional damage that "could last for years".
I had occasion to call in on Ms Whirlwind at her single sex boarding school yesterday and the girls were puzzled by it.
"We see plenty of boys," they told me.
They do too. Not only do they have they usual range of male relatives but they mix with other schools, including an all male school. They have mixed social events. They go on outings together. The Whirlwind has mixed with the boys in her street all her life.
But school? No. They were all quite firm about that. They preferred to keep the classroom to themselves.
"Boys don't learn the same way," they told me. It was an interesting comment coming from young teens. They may be right.
"And they are not as grown up," one girl said. Yes, she is almost certainly right about levels of maturation. They do differ. It is interesting she should have noticed that.
The Whirlwind's school does very well in science. It is not something the Whirlwind is particularly keen on but many of the girls do specialise in maths and physics in particular. They have outstandingly good teachers and that helps but they are also not competing against boys who tend to get the attention in class.
"And you know," the Whirlwind told me as we went back to the school gate, "We don't have to worry so much about what we look like. I mean we still have to be sort of tidy but we aren't competing for the boys all the time."
"Yeah, my Mum went to this other school with boys and she says all the girls used to do things like put their hair in rollers at night. Weird!" one of her friends told me, "It used to take them forever every night."
Oh yes, I remember that. My boarding school was co-ed. The competition was terrific - in the proper sense of the word. I hated it. The girls actually had their hair measured. It had to be an inch above your collar. It was supposed to stop all the nonsense with rollers and competition for the boys. It did nothing of the sort.
I can remember the traumas when partnerships broke up. I avoided the worst of it by spending weekends with my grandparents. I loathed school at that point.
But - I never had my hair measured. I arrived at school in a later year than the other girls. My hair was long and I insisted on leaving it that way. I had always had long hair. If they didn't like it that way then too bad. They didn't like it but there was nothing, short of ordering me to have it cut, they could do about it. That was a step too far even for that school.  
I never bothered with rollers and I refused to wear ribbons in the school colours. I wore ribbon covered elastic (made by my paternal grandmother) instead.
I was probably the only girl not traumatised by my appearance or the opposite sex at some stage because I simply did not care. I had other much more serious things to worry about.
The Whirlwind has plaits in school and about half her friends have plaits or pony tails in school as well. On the whole they look tidy. They keep their shoes and fingernails clean and then they get on with life. I don't see them as being traumatised by their appearance or the lack of the opposite sex in the classroom. They can go out in "civvies" and look good.
Of course there are arguments for and against both single sex and co-ed schools but to suggest that one sort traumatises students and the other doesn't is, I suggest, nonsense.