There are. The MCAT course section has a ton that helped me ace my sociology and psychology courses in college. YouTube has self-made Khan Academy playlists for psychology and sociology. 

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2. Content Requests and Feedback
3. Why are there no psychology/psychology related courses/classes?

Khan Academy Kids is a great start and then the grammar course here is very strong once they're ready. I would say a third grader can do it, but it may help to have adult support to make it fun. 

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3. Grammar Grade Levels?

I second this request

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3. AP courses