I do not teach to the Elements and Principles of Design. They have merit. Elementary students should definitely know them, but a project should not be about learning line, understanding form, or creating balance. Art projects are about making art. The Elements and Principles are part of that, but secondary.
I didn't always teach that way. The Elements and Principles of Design seemed like the only tangible thing I could be sure my students were "getting" from my class and I was crazy about making sure we covered them all and understood them undoubtedly.
We made terrible gradient lines, boring cardboard forms, and sooo many symmetrical shapes.
Around that time I made this packet. This seven page packet gives little exercises for each of the Elements of Art. Most of these are simple exercises art teachers have been doing forever, and some of the ideas (I think?) were inspired by Daily Warm-Ups: Art. Which, by the way, I do not recommend for elementary teachers at all.
The Elements of Art packet would not be too difficult for fourth and fifth graders to work on independently as a refresher, early finishers, or an end of year quiz!