You can see it early.

Today was a children's fair. I took a cool sciencey thing to show, but sciencey thing is not a toy, even though it may look like one. It costs as much as a very used car.

Ideal situation: child approaches, I introduce sciencey thing and allow child to touch and experience in a controlled manner. Child wonders in amazement and laughs at my jokes. I feel like I'm saving the world through science education.

Frequency of ideal situation: 45%
Frequency of children who approach sciencey thing aggressively and grab without permission, often under the direction of parents: 15%
Children completely uninterested in s.t.: 20%
Children grossed out by or afraid to approach s.t. 10%
Frequency in which child approaches aggressively bringing hand directly out of a food item to touch s.t. under observation of parents: 10%

And here's my favorite. Son approached s.t. with wonder in eyes and begins exploring nicely. Mom yanks son away to next booth saying "Hey! Is that one of them snap bracelets?!!? They're free!!"

I spend many, many synapses wondering/worrying about the importance of early childhood education, the achievement gap, etc. Why do some kids arrive on campus grossly undercurious? Why are some of my students so underprepared intellectually? Is it too late to help them by college? And a heartbreaker: highly motivated that simply can't retain information at a high enough rate to succeed. It seems that I got a glimpse into the "nurture" aspect of the phenomenon today.