I've thought about this a lot. The evidence seems pretty strong that as long as you are a reasonably decent parent (IE, maybe anything short of child abuse) your kid will probably turn out as their genetics and the large-scale culture predetermine in a lot of important ways: IQ, income, educational achievement. However, good parenting can make the journey more pleasant for everyone involved, even if the destination is roughly the same. If I let my son watch a ton of TV instead of actively playing with him it might not affect his adult IQ much, but I do think it would make both of us worse off and less satisfied in ways that would be hard to quantify. Of course, that may just be how I justify doing what my culture tells me is good parenting even though there's not much data in support of it.