Allow different users to upload pdf to nodes privately I am trying to build a question answer site in drupal 7. User with teacher role will create a question node, after that users with student role can upload answers in PDF. Different students can upload/attach their respective answers pdf for that question node.

Teacher after evaluating uploaded answer pdf will upload evaluated/corrected pdf for each student. Students can not view other students answers pdf or corrected pdf.

I am thinking to create a question content type and answer content type. Each answer will be linked to specific question node. Answer content type will have two file fields, one to upload answer pdf and another for corrected pdf.

Is my approach correct? Is there any better approach or any module which can help?
Creating two content types "Question" and "Answer" seems to be the right approach per me. These two could be related via entity reference fields. And the storage of the file fields should be "private" for the implementing the access control. I have recently written about private files in my answer you might check out.