When a teacher is grading an "Essay" type of Assignment they have the option of selecting: "set essay back to draft" so that students have to resubmit their essay. The submitted essay then disappears from the teacher's view. The student can now see the draft in their view and make corrections and resubmit.
It would be beneficial for teachers to always be able to see the original submission. When the student resubmitted, Populi could either replace the initial submission with the new submission or even better (like "File" type Assignments) both the original and the new submission would show up for the teacher to see.