Can a 16 year old in California decide not to go school when they have been the IEP program since first grade?

No, a 16-year-old in California with an IEP cannot unilaterally decide not to go to school. While they have more say in their education as they get older, they don't have the right to simply drop out. The IEP process itself is designed to ensure the student receives an appropriate education, and leaving school without a plan would violate that.

Even with an IEP, California's compulsory education laws require students to attend school until age 16. While a 16-year-old might be able to influence their IEP and the services they receive, they cannot simply refuse to attend school. Their parents or guardians, along with school officials, would need to be involved in any decisions about changing their educational plan, including potential alternative educational settings. Leaving school without a proper plan risks serious consequences, including legal actions.