Multitasking while studying: Divided attention and technological gadgets impair learning and memory. - Slate Magazine

Not just young people; also see Brain, Interrupted (NYT)

"Young people think they can perform two challenging tasks at once, Meyer acknowledges, but “they are deluded,” he declares. It’s difficult for anyone to properly evaluate how well his or her own mental processes are operating, he points out, because most of these processes are unconscious. And, Meyer adds, “there’s nothing magical about the brains of so-called ‘digital natives’ that keeps them from suffering the inefficiencies of multitasking. They may like to do it, they may even be addicted to it, but there’s no getting around the fact that it’s far better to focus on one task from start to finish.”"

Multitasking while studying: Divided attention and technological gadgets impair learning and memory. - Slate Magazine