This study examines a fifth grade science teacher's attempts at integrating engineering design using the construct of uncertainty. Collaborative action research served as a supportive mechanism to uncover and confront the teacher's uncertainties. Data were gathered through semi-structured interviews, reflections, classroom observations, lesson plans, and student work. Data analysis entailed the use of grounded theory. Findings from this study revealed that teaching science through engineering design is both challenging and problematic. Underpinning the teacher's pedagogical experiences was the constant force of uncertainty, in various forms, and how her sense of doubt was beneficial rather than problematic.