While your teen is developing into a young adult, it is very normal for them to not know exactly what they want to do with their life. Your teen may not even know when they graduate high school - and that's okay! It is not normal, however, for a teen not to have any direction at all. Your teen should have hopes, dreams or thoughts about their future.
Generally, teens get ideas about who or what they want to become and they start making plans in high school. Sometimes these plans are realistic, sometimes they are not. This is very normal behavior as it will start to point to a direction that a teen is going to take towards their future. When a teen starts looking toward their future, school and grades start to become more important. Teens who avoid thinking about what is ahead of them tend not to care about their school work, what classes they should take and what they should be learning.
If you have a teen that lacks a view of the future, you can help them by seeding some dreams through cool experiences that involve your teen's interests. Ask people you know about their careers and tell your teen. For example, if your teen's aunt is a chemist and gets to blow things up for a living, your teenager will probably find it interesting. If your teen does show some interest, set up a conversation between the two - then hide all of the baking soda in the house!
Here is a fun trick that I like and use on my kids: asking "I wonder" questions. For instance, when your family goes to an airport, and you see a cool jet, ask your teen: "I wonder what someone has to do to be allowed to fly that thing." Try one of these out on your teenager this week and see what they begin to wonder.
If your teen would like an idea of what jobs and careers would interest them, they can take a career test at the Princeton Review. From there, they can look at the Occupational Outlook Handbook to see what different careers pay and what schooling is needed to be in that career. You can also send away for catalogs to different technical schools and colleges.