Grade the project work. Teacher grades the scripts, short films and portfolios. The project progress and self-reflections presentations were graded earlier on in the project.
advertises this at the school.
Show the best films of each class (the ones selected by popular vote of the students and/or those with the highest scores of the teacher) in a school Short Film Festival for students of all years and teachers. Have small trophies ready for the winners in categories like "best film" and "best actor". Winners could be selected by a jury of e.g. English teachers in advance.