How Prototyping Practices Affect Design Results (via Stanford University)
Excellent video presentation that includes problem-solving exercises that empasise creativity. Being a Stanford University resource this concentrates on College/University students, but the examples seem like they could be adapted easily for lower grades.
(January 15, 2010) Steven P. Dow of the Stanford Human-Computer Interaction Group discusses his research on how prototyping practices affect learning, motivation, communication, and outcome in design. To help answer this question, he has developed creative problem-solving tasks, such as an advertisement design task where design creations are to be compared through ad campaign performance analytics.