There is an increased interest in integrating engineering design into K-12 classrooms because it equips students to solve real-world problems. However, before students are introduced to real-world problems, K-12 teachers may need to develop inquiry pedagogies and establish a learning context that supports student problem-solving. This study explored how a K-12 teacher engaged scaffolding practices to support students' design problems--ill-structured problems that offer multiple solutions--in a project-based learning (PjBL) environment. I leveraged a case study design to explore how a K-12 teacher organized and presented a PjBL curriculum to support students' design problem solving as they built prototypes of greenhouse to engage issues of food production and environmental sustainability. Both PjBL and design problem solving require instructional scaffolding so students can learn appropriate design principles that mitigate task complexities for authentic learning contexts. Based on the data (observation field notes, teacher interviews, teacher debriefs, researcher memos, course contents, and student artifacts), I identified two levels of influence that seemed to contribute to the teacher's planning and execution of this project: scaffolding practices and learning modes. A wide range of scaffolding practices surfaced while supporting student design, such as modeling, questioning, coaching, feedback, and reflection. Results suggest that the teacher integrated multiple subject areas into a central project and provided multiple supports at different times using multiple mediums to minimize task complexities. Additionally, the teacher mediated student learning by teaching iterative design principles and engaging them in prototyping. Finally, the teacher guided students to solve design problems through refinements. However, the teacher reported group dynamics, time management, and availability of resources as prevailing obstacles for the project. Nonetheless, the results suggest a student-centered classroom environment that considered low-fidelity prototyping, engaged in reflective feedback, and incorporated multiple subjects into a single project where the teacher's scaffolding practices might have influenced positively the inquiry process. [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.]