Auto insurance companies require all licensed household members be listed on your car insurance policy. Since this person has access to the vehicles of the house, they are a risk factor that insurance companies are allowed to include in their rating calculations.
While a friend may occasionally borrow your car and be covered, they do not normally have regular access to your car and thus aren't rated as a risk factor on your policy. If you do have someone outside of the household that regularly drives your car, then normally an insurance carrier would also want this person listed as an occasional driver so they would be properly covered in an accident. (See "Who can drive your car?")
Also, not all policies provide coverage to anyone that drives the car. Policies can have driver exclusions. These exclusions can include those under a certain age (under 21 or 25 for instance), unlicensed drivers and those driving under the influence -- to name a few.
Insurance providers thus require you add your teen since he or she lives in your household and is a risk factor to them. State laws permit an insurer to consider all resident operators of an insured vehicle when rating an auto insurance policy. This includes your child, even if he or she has only a learner's permit and especially when they have a full driver's license.
Insurance companies are usually allowed to use classifications that reflect a possible exposure for liability on the part of the insurer, in the event that bodily injury or property damage occurs due to the operation of the vehicle by anyone in your household, including your child.
Many parents would like to avoid the rate increase from adding their licensed teenager to their auto insurance policy; however, if you do not inform your insurance provider of your child's licensing status and your teen is in an accident, the incident may not be covered. In some states, an insurer may be allowed to cover the accident but then charge you for the premiums you should have paid up to that time for the teen to be on the policy.
Also, purposely not reporting a household licensed driver to your insurance carrier and adding the individual as a driver can be construed as misrepresentation, a form of insurance fraud.
Teen drivers are expensive to insure since they are inexperience and often immature drivers that statistics have shown are more apt to be in accidents. There are ways in which to help bring down the rate increase you receive from adding a teen to your insurance policy.
You can ask your agent about discounts for your child getting good grades (a good student discount), taking a driver's education or driver's improvement class, and any other discounts that your specific insurer has available for you to take advantage of such as a multi-car discount.
If you need to add a teenager licensed driver to your car insurance policy, then you need to comparison shop to make sure you and your family are getting the best rates possible. (See "3 ways to save big on car insurance")