Just at the end of my primary school days, there was an outburst of note-writing among the girls along the lines of "I'm not going to be your friend because you sat with x at lunch time."
This progressed to snide remarks we'd now regard as bullying and many of the notes were passed in a class of 48 so could be read by the passers-on, which, of course, we did as that was part of the aim of risking doing it in class. One of mine was snatched from the line by a teacher and - although I did not get belted (the usual punishment, which was why it was a risk), I got a severe telling off for my spelling mistakes and had to do the next spelling/dictation exercise using one of those wooden-handled nib pens and ink from the inkwell instead of a pencil which could be rubbed out.
Most of us turned out OK, becoming caring, responsible adults. We all do things we'd rather forget when we are young.
At a funeral recently, the mother of my best friend told me cheerily she'd come across "those horrible notes that youse used to write to each other in school". She couldn't believe how nasty we all were. I remember turning bright red with adult shame and regret.
I feel so sorry for the young people who not only have the right to make childish mistakes, but hold in their hands technology which can be misused at times of teenage passion and/or and used in stark evidence way into their futures.
They are also walking around with easy-use cameras, something that would have messed with our heads 40 or 50 years ago.
I agree with the others here who say it is essential that the parent hears it from home before they hear or see it from the other family or the school. But oh my goodness I am so sorry these children have phones when they are still at the silly note-writing stage.
And my family is just as bad as anybody else's. I don't know what the answer is. I think my age group were lucky.