I think if they are intelligent, intrinsically motivated, and willing to pursue knowledge beyond what the class requires, it probably helps. That last part is

I think if they are intelligent, intrinsically motivated, and willing to pursue knowledge beyond what the class requires, it probably helps. That last part is key. Intrinsic motivation doesn't mean you pursue it outside normal bounds. My kid loves soccer, its her second favorite thing in the world, she has an absurdly high tolerance for physical discomfort while playing, but she doesn't play it at home. There's other things she's rather do, such as play with her toys. When you move the bar to something even less interesting to most kids like science, you're going to have a pretty huge falloff. You're basically selecting for kids who choose to do it in their spare time. I know a lot of smart kids (I run a boyscout troop, my wife a girlscout troop, both with lots of high achievers), and none of them do this.