California DMV Practice Test
The California DMV provides lots of resources specifically geared towards teens. They offer sample driver license written tests as well as an interactive knowledge review to use as a study guide when preparing to take the written exams.
The California DMV also offers a lot of information specifically for new drivers. If you have any concerns or questions about the experience you should expect when going to the DMV to take the written test you should be able to get them answered there.