Sleep. A 12year old should be sleeping 9 to 12 hour of sleep a night.
About 8 hours. Sleep for kids is of vital importance, but seems to be an old fashioned discipline now. I see young kids out with parents at late hours when they should be in bed. In 7th grade he/she is a physiological adult and most adults require 6 to 8 hours. There is medical evidence that over and under sleeping as a life rule decreases longevity.
Varies some. The basic sleep requirement of a growing kid this age is a minimum of 9 hours.Extra studying,sports or practice can add to the need. Failure to get adequate sleep at this age leads to decline in academic or sports performance, sleep walking, sleep talking to name a few issues.