Yet another story where parents think they know best and are installing into their kids they are always right.
Rules are rules, its a couple of days in this country so they need to just get on with. I doubt very much the teachers were wearing shorts, probably why they are not in the photo anywhere.
And on the subject of shorts I wonder how many of these boys would want to wear a 'uniform' pair, they are probably thinking more of football shorts which is not acceptable.
I had to wear my blazer and full uniform all the time as it was a private school, and I was at school in 1976 which has similar temperatures.
Had a pair of shoes with a compass in them too, I'd forgotten them Mickey.