In my primary school in Australia, there is a saying with hats.
''No hat, no play.''
Then people start mocking it by adding the lines,''No school today, take your bags and go away.''
Well I guess, if you were to wear a hat indoors, it is rude, but if it's outside, wearing a hat is important as it shades your face from the burning sun, and then comes the sunscreen.
If you were playing under the sun without a hat, the teacher would either make you sit on a seat in the shade and be monitored not to move away from the seat (unless you need to go to the toilet or something), or if they're nice enough, to let you play in the shade.
Well, that's experience for me in primary school. smile