A marathon documentary about a veteran schoolteacher and his multicultural class of 12- to 14-year-olds in Stadtallendorf, central Germany, this extraordinary film, which won last year’s Silver Bear jury prize at the Berlin film festival, follows the tradition of observational humanism popularised by such film-makers as Frederick Wiseman and Michael Apted. It’s an investment in time, certainly, but this profound and hopeful picture justifies every second of its three hours and 38 minute running time.

Dieter Bachmann’s teaching methods are unconventional – he leans on storytelling and music in a classroom that has a full drum kit and is lined with guitars. But as an early scene in Maria Speth’s sensitive portrait shows, his approach is uniquely attuned to the needs of his students, many of whom are recent migrants who are not yet fluent in German. Herr Bachmann spins a surreal story of sentient furniture and musical instruments, and gradually the deflated kids perk up and engage. Ultimately, however, this is not just a celebration of one man, but of all teachers who go above and beyond for the children in their care.

• This article was amended on 12 December 2022. The Silver Bear prize is awarded at the Berlin international film festival (Berlinale), not Cannes as an earlier version said owing to an editing error.