I'm surprised that everyone seems to address everyone else as "tu" instead of using "usted" to adults and strangers. Is this just a quirk of this show, or is it normal in Spanish schools?
shareI am fairly certain it's normal in Spanish schools for students to both use tú with teachers and use teachers' first names.
shareI'm from Colombia and our use of "TU", "VOS" and "USTED" are very different than in other countries, our is more regional, but I have the impression that in Spain (and in Mexico as well) the use is very distinct having to do with "TU" being used by someone addressing another person who they deem either as equal or inferior (inferior not being necessarily below, but also towards younger people). "USTED" is more to another person you respect or older people.
That being said, the dynamic changes a little bit if you are from the upper higher class; if you are like this kids who belong to rich families (maybe sometimes middle upper class) then everyone treats each other as equals, even with teachers and older people, but this is only a modern issue, in the past it wouldn't be allowed.