During the early years of formal schooling it was common if the teacher was busy and a younger student needed help that an older student was asked to pitch in and lend a hand for a little while. This was mainly due to the fact that there were not as many 'qualified' teachers available.
This is also true during the time of my studies. I do not know if it it still true today.
Depending on which country you live in, it's quite possible this still happens.