The teacher has control over allowing the student to resubmit their work. The pre-existing controls to lock a submission to prevent further work on it are still there.
However, there are no controls to allow a user with higher authority than the teacher to lock the grade and prevent the teacher from changing it (although there is an option to limit the total number of resubmissions allowed, which a non-editing teacher would not be able to edit). There are a few descriptions you can find out there on the internet that can lead you through how the resubmission feature works, but here is one that you could look at: http://www.synergy-learning.com/blog/moodle/moodle-2-5-improvements-assignment-resubmissions/ (note there is a fairly obvious bias in pointing you at that blog post ).