I found some great sites for instruments measuring intrinsic motivation. It always helps to know you don't have to reinvent the wheel. All 3 of my classes this semester have been very practical. I have accumulated a great deal of relevant, useful resources.

I still would like to measure creativity, even though I know it is difficult to measure. If I control for intrinsic motivation, perhaps by giving a post test with a high level of test retest validity after 2 projects, and then qualitatively look at the levels of creative thinking evident in the 2 projects, this could be a mixed methods approach.

The research problem becomes: Does intrinsic motivation affect levels of creativity in the high school art classroom?
If the intrinsic motivation is the same then creativity levels should stay the same. If they vary, then intrinsic motivation does not  play a large role in affecting creativity levels.

Let's look at it another way:
Use intrinsic motivation, test for it, when assigning one project (or in one class doing the same project) and then an external motivator for a different project (or different class doing same project project as first class).
Assess levels of creativity.
Research problem could be:
Do extrinsic motivators affect the levels of creativity in the high school art classroom?

Few points to consider about validity:

• If 2 classes are used how could I assess that the beginning levels of creativity are similar amongst the students in each class?
• What type of extrinsic motivator could be used? Contest with prizes are motivators in the art classroom. Grades could be used I suppose. One project they know they will get a grade on, and one they are told they will not.
• If two different projects are used within the same class, how to determine that both will produce the same levels of creativity without factoring in the motivators?

CREATIVITY by Mihaly Csikszentmihalyi

"Twenty-five centuries ago, Plato wrote that the most important task for a society was to teach the young to find pleasure in the right objects. The problem is that it is easier to find pleasure in things that are easier, in activities like sex and violence that are already programmed into our genes. It is much more difficult to learn to enjoy doing things that were discovered recently in our evolution."

"It is in this sense that creative individuals live exemplary lives. They show how joyful and interesting complex symbolic activity is. They have struggled through marshes of ignorance, deserts of disinterest, and with the help of parents and a few visionary teachers they have found themselves on the other side of the known. They have become pioneers of culture, models for what men and women of the future will be—if there is to be a future at all."

CREATIVITY by Mihaly Csikszentmihalyi

"This is a journal of your thinking and resources related to your research interests and what will hopefully end up as your dissertation topic. It is not meant to be written for a particular audience. You are the audience. It is your "notes to self" and to me, about your investigation of research problems, and the process of focusing on a particular area of research."

IDT 8600: Seminar in IDT Research Dr. Trey Martindale