I had penpals when I was young, it wasn't done through school though, I think there was some international penfriend organisation that you could write to with your details and they would put you in touch with people. I had three - one in New Zealand, one in Sweden and one in Italy. The NZ and Swedish one I kept in touch with for a few years, the Italian not so long. I still remember their names and even the address of the Swedish girl! It just sort of fizzled out, nothing to do with the internet, this was back in the 70's.
3b in South Australia.