Hi SuperB,

Thanks for writing in with your feedback! I understand the concern and confusion you must feel as there's no Mastery for the AP Chemistry course, but the units in the course do have. We’re always looking to make Khan Academy a great learning experience.

While we wish we could implement all of our users' requests, we need to make difficult decisions about which features and requests are aligned with our goals at the time.

As our needs and resources change, it’s possible that we may be able to revisit this issue at a later date, but I can’t guarantee that we’ll be able to do so, or provide a timeline for when that might happen.

Thanks again for your interest in improving Khan Academy :)

All the best,