The purpose of this qualitative study was to explore two elementary teachers' implementation of engineering design over two academic years and to describe how their teaching practice changed over the two instructional cycles. This study used field notes and audio transcripts of the teachers during their engineering design teaching, written reflections, and a final interview to generate data that were analyzed for emerging themes and patterns. These data answered the following research questions: (a) How do two fifth grade science teachers implement an engineering design activity? (b) How do these same two fifth grade science teachers' instructional practices change as they implement the same engineering design activity for a second time the following academic year? And, (c) What factors do the teachers identify as to why their practice changed? The findings of this study concluded that with experience teachers made more explicit connections to science and engineering content and practices. Additionally, they more actively facilitated deeper questioning and troubleshooting. An additional finding was that teacher change is not an isolated event, but a system of interacting influences. The findings in this research study provide insight and implication for supporting teacher change in practice in K-12 educational reform efforts as we move to implement engineering and engineering design into the K-12 science curriculum. [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/en-US/products/dissertations/individuals.shtml.]