MrMobius

Maybe your teacher uses vous not as a formal address to one student but rather to speak to the whole class? Or he/she respects some students more than others and uses vous to talk to them, in spite of the age difference.

In French/France I use the formal vous when talking to strangers or customers. Here people generally switch pretty quickly to the informal tu when they get to know each other (at my first day at work with my colleagues and boss). But I’m quite an oddball since I use the formal address even for kids, which no one does. Also my neighbor was a bit annoyed at me for continuing to say vous to her after having met her one month ago. It can make people feel old.