Since Moodle 1.7 a number of options in Database have been migrated over to the Roles system. For example, preventing students (or any other role) submitting data must be done by overriding the role for that particular instance of the Database. However, do note that by default teachers are unable to override roles and this ability must first be granted by your Administrator for the course or site as appropriate.
That sentence probably prevents piles of queries of the "I'm a teacher and can't find how to prevent students from submitting data to Database" variety.