I don't think that the two things need to be mutually exclusive.
Working in a classroom can teach all sorts of 'non curriculum' stuff, like groups work, taking turns, sharing, basic manners etc.
The difficulty with (and for) some children is that they don't come in with the fundamentals for this sort of stuff in place. And in some cases the parents actively encourage the children to ignore some what is going on in the classroom.....small numbers granted, but the effect of these children can be considerable.
I'm thinking of a case of a bay who was very disruptive (at the age of 11) in a particular subject. When I discussed the issue with the father and the boy the father excused the boys behavior totally because 'Well I didn't like that subject when I was in school either' . At which point both he and the boy smirked. So I told him that while I couldn't expect his son to like everything, I could expect him to behave, if for no other reason that he was wrecking the class for children who did like the subject. This possibility had never occurred to the father, and naturally had never occurred to the son.