Ongoing efforts across the U.S. to encourage K-12 students to consider science, technology, engineering and mathematics (STEM) careers have been motivated by concerns that the STEM pipeline is shrinking because of declining student enrollment and increasing rates of retirement in industry. The Enrichment Experiences in Engineering (E[superscript 3]) for Teachers Summer Research Program at Texas A&M University engages high school STEM teachers in an engineering research experience so they can introduce engineering concepts through the courses they teach to their students and stimulate students to pursue engineering careers. This paper presents programmatic evaluation mixed-methods findings assessing the value of the E[superscript 3] program as a catalyst for STEM teachers' professional development in understanding the field of engineering and their perceived ability to implement engineering content into their high school STEM classes. Quantitative programmatic evaluation findings document that the E[superscript 3] program had a positive benefit for STEM teachers as related to their experiences in teaching and promoting the field of engineering to their students. Qualitative programmatic evaluation findings document two themes, "Positive Professional Development Growth" and "Short/Long-Term Benefits of Participation." Finally, recommendations are provided to high school STEM teachers and Colleges of Engineering to enhance their partnerships.