This quantitative quasi-experimental study, adopting a pretest/post-test control/treatment group design, investigated the efficacy of instructional strategies for developing divergent thinking in gifted and talented students within K-6 heterogeneous cluster classes. It specifically explored the problem of insufficient evidence-based approaches for fostering divergent thinking, an area often neglected in traditional gifted education programs. The study was grounded in the Triarchic Theory of Intelligence, which emphasized the importance of creative intelligence as a domain equal to analytical and practical intelligence. The primary research question focused on the extent to which a targeted divergent thinking instructional approach, derived from the Williams Model, impacted students' divergent thinking skills. Participants included 269 students of varied abilities from New Jersey public schools, with the sample determined through power analysis to ensure a 0.90 power. Data were collected using the Williams Creativity Assessment Packet (WCAP), administered by trained teacher facilitators before and after an 8-week instructional intervention. Findings revealed a statistically significant increase in divergent thinking among all students, with gifted and talented students showing the most pronounced improvements. The study identified themes of increased fluency, flexibility, originality, and elaboration in students' thinking. Recommendations for future research include replicating the study with alternative assessments, extending the duration of interventions, enhancing WCAP's scoring system, modifying its format for diverse learners, and periodic re-norming to reflect current educational contexts. This investigation helped identify a possible formative assessment strategy for students receiving gifted and talented services. Norm-referenced creativity assessments can be effectively integrated into gifted and talented programs to nurture divergent thinking, providing a more comprehensive evaluation of student capabilities. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]