not necessarily true.

I know/hear many kids did not pay too much attention during their first 1-2 years. When they realized it, it is already too late. For a kid only 14, 15, his mind is far from mature, even though he can be super smart/talented. The way of the US system is to select the kids who get matured early, who pays more attention to details during daily time, so on. That is one reason y many talented kids cannot go to top schools, and many top sucessful people do not graduate from top schools. The system in the US is to choose the people can constantly be good at taking exams. You almost need all A in high school to be able to get into top schools; of course there are exceptions.