FarNorth
^Google '1960s women in trousers' to find pages and pages of other images, including links to sewing patterns to make your own, which suggests that they were very mainstream. I think these all have centre zips, too.^
Trousers for women weren't acceptable in most jobs, as far as I remember, in the 70s and in some not until a couple of decades after that.
No, but they weren't prohibited by law, and they weren't groundbreaking in the 1970's, which were the arguments used to demolish any idea that a man wearing a skirt is not a neutral act in the current climate (50 years later). I was a child in the 60's, but remember my mum wearing trousers, and she won't mind me saying she wasn't a 'fashion plate' to use a 60's term 
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I was a teen in the 70s, when 'gender bending' began (in popular culture, at least) and whilst 'the establishment' grumped and grotted, it quickly became mainstream for a lot of young people, but not in the workplace unless you were a fancy hairdresser or worked in the sort of places I could only dream of - ad agencies and the like. I was briefly a civil servant in the mid-70s, and remember being told that women could wear trousers in the office. It hadn't occurred to me that we might not have been, as everyone I knew wore them a lot then; but obviously they must have been forbidden until soon beforehand. A boy or young man turning up dressed like David Bowie on the cover of Hunky Dory would not have been accepted though, although I very much doubt there was anything in the contract to forbid it. Here's a gratuitous picture of the lovely David on the cover of The Man Who Sold The World, as it shows his dress more clearly (this is the one I own, fact fans - I was in the car when I posted earlier and got them mixed up). He wears a dress on both, I believe, not that it matters.
As ever, though, the diversion has become the main topic. What happened in the 70s is irrelevant - I fall for it every time .
To return to the skirt-wearing teacher - in my opinion (others' may vary)
*Man wears skirt = not an issue
*Man wears skirt to teach primary children = okay(ish), but don't expect them to conform to uniform rules in secondary.
*Man wears skirt to teach primary children in an atmosphere where 'gender' issues are being pushed at them in various ways, and they are told that 'gender' can change, regardless of sex = Not Fine At All.
