Translation:The girl has taken three classes about Danish history.
I've never seen nor heard "klasse(r)" being used this way in Danish.
Is it correct then?
I wouldn't say so, no. Can't find the used definition in a dictionary either. But Duolingo obviously disagrees.
As I can see you are a Dane so maybe I should believe you, not Duo :)
It is not used correct
Why "lessons" for "klasser" does not work? Seems like a synonim to me.
lessons indicates one days worth. In a class, there are lots of lessons.
In the UK it could refer to either.
"Klasse" means grade in Danish