Not a teacher, but I've found this:
fromThe plural form peoples logically refers to more than one community or nation, although down the centuries some writers have been chary of it, and in the nineteenth century one described its use as “uncouth”. These days it is the accepted form in contexts like “His authority shaped diverse peoples into common views and allegiances” or “Magnified traditions especially bolster peoples embittered by subjugation or newly come to nationhood”.
World Wide Words: People Versus Persons
Hope it helps
Student or Learner