[iamthebest]

But do they make a positive or a negative difference?

I would argue that my father had a negative influence. Mom wasn't really good or bad so I'd say she didn't make a difference.

I think Neil Tyson's observation that he experienced success in spite of his teachers, not because of them is worth pondering.

[mahyarm]

You could say the same thing about mothers or any sort of parent. Any parent can be a negative or a positive, but what is it in the general case of parents who care about their children?