Having raised three teens in the last decade I can speak with assurance that most young people believe they are good multitaskers. They will tell you they can listen to music, do a little social networking, and do homework while talking on the phone. Actually, they claim they can do more than my simple list :-)
The research just doesn't back it up. The brain requires a singular focus for what most of us call true learning. Of course people can do multiple things during the same few minutes, but that is not the same as learning or processing or thinking. Consider Dr. Cantor's remarks.