well i can't confirm if it's "widely used" but i was at a grammar school & we used to call them 'tutor groups' too.

We had tutor groups in my school, but this was the class for registration and other administrative purposes, we didn't necessarily have all classes together after the first year.

It was a private, day+boarding school.

However, surely they should learn the most standard word?!

Funny, I just came across the "tutor group", too, in the workbook "Learning English". My understanding of "tutor group" is of something smaller than a "Klasse", and I would expect a tutor to have less status than an official teacher. Am I entirely wrong, outdated, out of tune with real life in English-speaking countries? Help, please!

as Nicole said yesterday, in my experience the tutor group was for registration purposes and the tutor was generally someone who is originally only a teacher and takes on additional responsibility as a tutor.

as for it being old-fashioned, you're probably right, but i think the term is generally found in grammar schools, which - complete generalisation i know! - tend to hold on to old-fashioned terms.

hope that clarifies things a bit!