WHen one does a "work for hire" one HAS NO RIGHTS to the material. Work for hire comes in several types:
1) Stuff you created while being paid to work, provided it is part of your work load. (In my case, almost everything I've written after college. For example, I don't own my lesson plans, the school does.) They don't even need to credit you unless they agreed to do so.
2) Stuff for which you received a grade. It's owned by the person who graded it. Essentially, your grade in a course IS payment. They must credit you as a generality, but can release the work in print with no other compensation. (They may not release your grade, however...) Or, at least, in the 1990's they could. (I've not checked since then.)
3) Stuff you were commissioned to write. It's not theirs until they pay, but once they do, you have no rights to it. Residuals require a contract agreeing to residuals. Credit need not even be given unless it is contracted for.
4) stuff you sold after submitting to a call for works. Other than the fact that you weren't under contract when writing it, it's the same as stuff you were commissioned to write. If it isn't chosen, and the submission guidelines don't require you to surrender rights at submission*, you still own it.
*Many contests require assigning all rights to the work. But when a commercial RFP goes out with surrender of rights on submission, something is seriously wonky.