I've seen an adult with "teaching" as their activity, but no kids around...

A couple of ways that this can be improved:

1) Anytime the school drum is hit, there is also a "Master" who comes to the school to "teach."

2) If a "Master" gets a "teaching" activity, he/she should find a child or trainee with the same field checked and spend some time trying to "teach" that other villager. (Like a Doctor finds someone to heal.) If the teaching is successful (it might not always be) the student gains a little bit more skill.