Is it common to ask students to help the teacher in the teacher's normal duties?
Confucius once said (in a rough translation) "It's student's job to serve the teacher when the teacher needs help." (the source in Chinese)

I think in most places, where Confucius's principle is still being followed, helping the teacher in his normal duties is considered normal.

However, help marking the sheets is not normal as far as I understand. At least, Confucius never graded his students. He did have comments about his students, though.