Common sleep disorders seen in teenagers, and childhood include insomnia due to poor sleep hygiene, but they can also include primary sleep disorders, such as obstructive sleep apnea where you are not breathing well while you're asleep. So you're brain senses that, and keeps waking you up. This in turn causes sleep deprivation, and sleep fragmentation.
You can also have restless legs syndrome, where you have an uncomfortable feeling in your legs and you need to constantly move around to help you sleep better at night.
You can also have circadian rhythm disorders, such as delayed sleep phase syndrome. Now in this disorder your circadian rhythm is offset where you have a tendency to want to sleep later, and wake up later. Unfortunately, kids are not allowed to do that, because they do have school in the morning.
In teenagers, we are now seeing anxiety, and depression play a role in having insomnia at night. So it is important to have your physician fully evaluate your child, or teenager to make sure that none of these disorders are contributing to insomnia.