in reply to
How do I get my teenager interested in software development?
It didn't sound to me like talexb was pushing, given that he wrote that his stepson hopes to be accepted to study CS next year. To me that implies that there is interest. On the other hand, the last statement, about 'putting' him in Political Science or Journalism does suggest a bit too much involvement in what should be the stepson's decision.
I know a friend who does consulting lets his son handle some of the work, and receive the payment for what he does. Earning money is certainly inspiring (especially when it's far more than you'd make at a McJob), although I know a good many people who were inspired by good job offers to drop their studies!
I do agree with the others that you should probably ask him what he wants to do, and try to find a project personally relevant to him--be it a programming project or something completely different.