I agree. But I still think it is all more sensitive in children. They have less self control and it is easier to discourage them. As adult, I was more able to distinguish between "the topic is uninteresting" and "the class was badly taught".

Then again, children can learn by themselves when it is all framed as game they are freely exploring - adults learn much less that way.

Then there is a factor of developing brain - your students all have already brains fully developped. So it won't happen that someone does not possess abstract thinking yet, but still may suddenly click 6 month later on.

Basically, adults are more able to overcome obstacles and be independent in learning while children depend on teacher much more - both for motivation and actual content.