I agree with @skieurope that one does not need to have completed AP science to take the science SAT, although it is worth researching how the Subject Test content and one’s science class content overlap. My son took Bio subject test after taking 9th grade Honors Bio (not AP) and only had to teach himself a few topics. He still had to teach himself a few topics to take the Physics subject test this year, even after taking Physics C. The content overlap will vary by high school.