When Jen nods off in her morning calculus class, odds are that she really can't help it. Although she stayed up late chatting with friends on her computer, she couldn't have fallen asleep at 11 PM even if she wanted to. In fact, there are biological reasons teens shuffle around in the morning, only half awake and come alive in the evening.

Teens' circadian rhythms shift from a morning preference to an evening preference around the time of puberty. Their internal clocks are out of sync with their early morning school schedules. Research indicates that students become alert and eager to focus around noon.

How does this manifest itself?
Due to changes in teens' circadian rhythms, they may experience the following:

• Fall asleep in class
• Under perform on school activities and tests
• Appear groggy and grumpy
• Exhibit signs of sleep deprivation

How can teens reset their body clock?
Clinical research now confirms that bright light in specific wavelengths can shift the internal body clock and regulate sleep patterns when used for 30 to 40 minutes upon waking. A teen can reset his or her internal clock by receiving bright light exposure and thereby assist the body in suppressing melatonin during the day, which means he or she will feel tired at bedtime.