I am not a student, but a member of faculty and do not like the watermarks on the dwgs that are handed out to students.
Do you also object to students turning in their work with watermark?
2009 is a really ancient release and would not be subject to upgrade in any case.
Students (or faculty) with student license of 2012 can upgrade to commercial license simply by purchasing a commercial license and going to Help>About AutoCAD>Product Information and selecting Change Serial Number.
But of course, all work done with student license would have to be recreated on commercial license for commercial use.