When the lesson just does not work

This past rotation my fifth graders have been working on a picture called "12 things".  I put a list of objects on the board and they are to draw them.  The arrangement of the objects and how they are organized is up to them.  I give examples of different ways they can be arranged and what to do with the background, that their objects must be 3-dimensional.  All of these things that should not be that complicated for fifth graders, because the objects are things they would already know how to draw.  But the projects just never turn out that great.  I am always left disappointed with the way they are using their time or drawing their picture.  I don't think it is the student's fault either-I think it is just too open-ended. The concept is too broad for most of them to grasp.  Even some of my best artists seem to forget things they already knew when drawing this picture.  I think it might be time to retire this project.  To be fair it was a middle school project and I guess it is good to reflect from time to time what works and what does not.  Maybe I will be able to drag this project out another year--after I have forgotten how it did not work that great!