Was Claude's writing that good?
Much is made of his so-called promise, but while he was head and shoulders above his colleagues who wrote about pizza and their mobile phones, I didn't see any real literary genius going on there. No snappy aphorisms or startling phrases. Perhaps it 'reads' differently in the original French? All we get is what goes on in the household, which is interesting from a nosey perspective, but not a whole lot else.
Of course, maybe the teacher was looking for a son substitute and the couple were just bored and liked to live vicariously, but the teacher makes a big play of how the kid has talent, and he seems to believe that as the main reason for offering encouragement.