why would you be worried about the teacher touching the papers?
That's your takeaway?
While a remote chance of contracting covid exists on surface contact, it's still a chance. The teacher typically hands back papers. Thus mixing everything sneezed, coughed, breathed or finger licked into a big stew to be shared with his/her students.
WebMD: "How long will the coronavirus survive on paper? Examples: mail, newspaper. The length of time varies. Some strains of coronavirus live for only a few minutes on paper, while others live for up to 5 days."
CDC: "It may be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes, but this is not thought to be the main way the virus spreads."