The New York Times has an easy-to-read post of the dangers of insufficient sleep. It has lots of warnings that will trigger adult panic and cause your teen’s eyes to glaze over. Here are the relevant teen parts.
About learning, memory (important for test taking and studying):
Some of the most insidious effects of too little sleep involve mental processes like learning, memory, judgment and problem-solving. During sleep, new learning and memory pathways become encoded in the brain, and adequate sleep is necessary for those pathways to work optimally. People who are well rested are better able to learn a task and more likely to remember what they learned. The cognitive decline that so often accompanies aging may in part result from chronically poor sleep.
About looking good for the ladies:
Growth hormone is released during deep sleep; it … boosts muscle mass and repairs damaged cells and tissues in both children and adults.
About attention and focus:
[There is] evidence associating inadequate sleep with an erroneous diagnosis of attention deficit hyperactivity disorder in children. In one study, 28 percent of children with sleep problems had symptoms of the disorder, but not the disorder.
With insufficient sleep, thinking slows, it is harder to focus and pay attention, and people are more likely to make poor decisions….
About not killing people while driving:
[Insufficient sleep] can be disastrous when operating a motor vehicle or dangerous machine.
In driving tests, sleep-deprived people perform as if drunk, and no amount of caffeine or cold air can negate the ill effects.