The manufacturing industry is one of the largest employers in the US and plays a vital role in contributing to the US economic growth. The prospects of manufacturing growth and stability are the focus of many developed nations. However, the recent fast paced advancements in manufacturing technologies have created a void in the talent pool that requires a skilled workforce to fill in the gap. Prior research shows that the foundation of STEM education, including advanced manufacturing, is laid out during K-12 education. Further, high school teachers with higher self-efficacy beliefs are found to be more successful in generating interest and highlighting value of STEM education in their students. The prior research also reveals that, in addition to their self-efficacy beliefs, teachers' perception of manufacturing can also impact interest among their students. To that end, this research aims to investigate the impact of an intervention program (an engineering research and enrichment experience) on the self-efficacy of the secondary teachers. Specifically, this study focuses on impact of an enrichment experience in engineering (E3) program designed for high school teachers to boost their engineering/manufacturing self-efficacy. The paper investigates the teachers' understanding of manufacturing and how their perception about manufacturing changed after partaking in the E3 program. It uses the T-STEM instrument to evaluate the self-efficacy beliefs of E3 participants and to determine the effectiveness of the program. The paper also presents a comparative analysis of teachers' self-efficacy between various population groups divided by gender, ethnicity, and school type. The survey results show that the E3 program improved the self-efficacy of the teachers across all the population groups although with some variations among the groups in the net gain in post program efficacy.