As the press seem unable to find some photos of what schools actually look like at the moment, I thought I'd try to find some myself. They aren't current school photos but pretty much reflect the day-to-day.
1st is a typical classroom in terms of space. Fewer kids than normal though.
2nd is a typical corridor (except much cleaner). Yes they are wearing masks but they are also so close as to be touching. Note the kid with the mask half off, nose out, he has probably just been told to put it on by a teacher. What's unusual is that the kids all have a mask and none are being worn on chins. Also, they're on their phones. Tut.
3rd is what a typical break time looks like. Note the clumps of kids and the boys grappling. No masks, obvs.
Any ideas as to why secondary pupils are the most infected subset of the population?