A classroom example can reveal which households the teacher imagines as ordinary.

The examples a teacher reaches for describe a household. Two parents, a car, a holiday, a spare room, all offered casually as the ordinary case, and every child whose life differs learns quietly that theirs is the exception. Nothing has been said about them and something has been established.

Vary the examples deliberately, or keep them neutral about circumstances. It costs nothing in the lesson. And it is worth listening to your own defaults in any explanation, since they are usually a picture of your own life offered as the standard one.