I covered some of the technical issues in this post. If you want to give the students a read-only project, one way to do this is to compile the scenario, close Greenfoot, delete all the .java files (but retain all the .class files and image files, etc). Greenfoot will be able to open and run this project, but the students won't be able to see/edit/copy any of the source code.

Thanks for that; looking at the problem more holistically, have you considered using jlink to generate a complete self-contained application runtime? Be warned, this is not for the fainthearted - the compiled project has to be fully modular, including all dependencies, which can be a real pain (although there are plugins you can use to coerce non-modular libraries to become modular).