Ayaka.Sarah

1. Community
2. Classroom Tips and Tricks
3. Mark questions or sections for students

That's what the coaching function is for. You just need to become their coach. I'd show you a guide but I'm currently using a tablet so I can't, but since it's one of the main features on Khan Acad...

1. Community
2. Feature Requests and General Site Feedback
3. Mastery Challenges/Practice tasks

I agree with Adam. However he did not cover the "Plus, please do not put topics I have already Mastered in Mastery Challenges." part so I will. If you, say, master long multiplication in a week and...