To assign permissions for forums, click on the Administer | User management | Roles link, or navigate to admin/user/roles. We will be adjusting permissions for the Teacher and Student roles.

The forum module has six permissions:

Of these six permissions, only one, create forum topics, is a must-assign for site users. Additionally, most users will probably want to be able to edit own forum topics. However, it's worth considering that if a user edits a forum post after a comment has been made, the context of the comment, and the subsequent discussion, will be lost. For this reason, we generally recommend only assigning the ability to edit any forum topic—and either of the delete privileges—to very trusted users.

Once you have assigned the desired rights to both the Student and Teacher roles, click the Save permissions button to save...