“The fast-track kids didn’t turn out O.K.,” said Joseph P. Allen, a psychology professor at the University of Virginia. He is the lead author of a new study, published this month in the journal Child Development, that followed these risk-taking, socially precocious cool kids for a decade. In high school, their social status often plummeted, the study showed, and they began struggling in many ways. It was their early rush into what Dr. Allen calls pseudomature behavior that set them up for trouble.