According to the March 2005 Kaiser Family Foundation Study (p. 23):

Homework has also become a magnet for multitasking. About one-third (30%) of young people either talk on the phone, instant message, watch TV, listen to music, or surf the Web for fun "most of the time" they're doing homework. Another third (31%) say they do so "some" of the time.

P23, Kaiser Family Foundation's Generation M: Media in the Lives of 8-18 Year-olds

According to the Pew Internet & American Life Project, teens are using computers at school, at home and very likely while visiting someone else's home!