I think a childs grades in school depend much on the childs developmental abilities, which are influenced by too many factors, especially the environment in which they spend the majority of their time, to credit one particular social setting to an improvement in grades. Children do learn most by example, so if the Parents are careful about those whom they allow within the childs sphere of influence, that they imitate Christ in speech, behavior, love, faithfulness, and purity, it may be a key influence in their overall performance- But not everyone in a 'christian fellowship' imitates Christ - so the question for me is who am I allowing to set an example for my children?