STEM education is a national priority, and more schools are implementing STEM K-12. Elementary teachers are prepared to teach science, mathematics, and technology, but teachers may not feel as prepared to teach engineering. Engineering is a new genre for elementary schools, and it is not typically a content area included in teacher preparation programs. Therefore, teachers may not feel as confident to teach engineering. Teacher self-efficacy is a major variable in student achievement. The purpose of the current study was to determine if there was a statistically significant difference in math and science achievement in grades 3-5 and teacher self-efficacy in engineering. The study revealed mixed results. An Independent-Samples t Test showed a difference in the engineering self-efficacy levels and student achievement in mathematics but not in science. However, the body of research does support the importance of teacher self-efficacy in STEM and preparing students for the 21st century workforce. [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/en-US/products/dissertations/individuals.shtml.]