Integrating engineering and technology concepts into K-12 science and math curricula through engineering design project-based learning has been found to increase students' interest in science, technology, engineering, and mathematics (STEM), however preparing teachers to shift to interdisciplinary teaching remains a significant challenge. Primarily teachers need to develop both skills and attitudes toward interdisciplinary teaching. In doing so, professional development (PD) is considered a key component in helping teachers through this transformation process. In an educational environment of accountability, measuring the effects of PD programs on teacher behaviors and capacity is essential but often elusive. The current study describes the change in attitudes to interdisciplinary teaching of 29 self-selected middle and high school teachers who participated a PD workshop and in delivering a 12-15 week interdisciplinary teaching and design problem unit that spanned multiple STEM subjects. This quasi-experimental pilot study implemented a single group pretest-posttest design using survey methods to collect data from the participants at two intervals; at the time of the PD workshop and at the completion of the teaching unit that emphasized a long-term engineering design problem. The goals of this research are to (1) assess the changes in attitudes to interdisciplinary teaching, attitudes to teamwork, teaching satisfaction, and resistance to change, (2) explore relationships among these changes, (3) and describe the variation in these changes across teachers' gender, school level, discipline taught, and education level.