According to a Stanford sleep study, adolescents need nine hours and fifteen minutes of sleep, and children need 10. Lack of sleep can cause irritability and an inability to focus, so whether you're up late studying or chatting online with friends, enough sleep is important for any student. Power naps are ok during the day, as long as they're quick. Famous geniuses Albert Einstein and Leonardo da Vinci were known to take day naps, and doctors say that taking a 20-minute nap eight hours after you wake up is healthier than taking an extra 20 minutes to sleep in the morning.