Then he might be able to choose a daytime or evening habit that he thinks will help. Why teenagers need sleep Your teenage child needs sleep to: maintain a healthy body keep her immune system working well maintain good mental health boost her energy levels, learning and concentration store things in her long-term memory. A quiet, dimly lit space is important for good sleep. This will help her body produce melatonin at the right times in her sleep cycle. Most teenagers need hours of sleep each night. Encourage your child to do some physical activity during the day, but not too late at night.