The problem with I.Q.

Among other things, it isn't set in stone:

Teens' personalities, work ethic and the home environments are important, too. "There's a lot of variability in neural development during adolescence and in young adulthood as well," says Stephen Ceci, a professor of developmental psychology at Cornell University. He says this study should give educators and parents pause. "It should caution all of us against assuming that one low IQ score, at one time, is capturing all that an individual is capable of," Ceci says.

Like so many tests, its result is mostly no more than an indication of how good you are at...well, that test.