Fifty-three percent of 12- to 17-year-olds pursue at least one other activity while studying, and 21 percent keep busy with at least three tasks, a poll shows. Master multitaskers? Hardly, say experts.

In fact, teens who juggle homework with TV, e-mail, IMs and iPods may be short-circuiting their long-term brainpower. Opting for instant gratification (answering every e-mail as it arrives) over the completion of longer-term goals (finishing an essay), says Jordan Grafman Ph.D., chief of the Cognitive Neuroscience Section at the National Institute of Neurological Disorders and Stroke, can impede the development of the brain’s prefrontal cortex.

The section that controls social cognition, planning, conceptualization, reasoning and decision making, the prefrontal cortex doesn’t fully mature until the mid- to late 20s. Besides, as Dr. Grafman points out,“No one can deliberate, acquire facts or truly learn if he’s flitting around doing a dozen things at once. Successful multitasking is about prioritizing and using technology judiciously.” What can parents do? Enforce a no-gadget rule—at least until the homework is done. — K. Emily Bond