With the heightened focus on STEM education in school districts, there is a need to examine the professional learning provided to teachers who implement STEM curriculum, especially low-cost, sustainable professional development experiences. This study used an embedded mixed-method design to examine the connection between Guskey's model of teacher growth and the Japanese Lesson Study cycle, and the relationship between teachers' sense of self-efficacy and collective teacher efficacy for elementary teachers implementing STEM lessons. The four research questions were: Does participation in a STEM professional learning that includes Japanese Lesson Study increase collective teacher efficacy? Does participation in a STEM professional learning that includes Japanese Lesson Study increase teacher self-efficacy? Do outcomes differ between a lead teacher and an observer teacher in STEM professional learning that includes Japanese Lesson Study? What are the perceived aspects of STEM professional learning that includes Japanese Lesson Study that foster collective teacher efficacy? Thirty participating elementary teachers experienced two different low-cost, professional development experiences. Each experience included PD workshops on design thinking and teachers implementing a STEM lesson independently and collaboratively through the Japanese Lesson Study cycle. Quantitative data were collected four times using the Collective Teacher Beliefs Scale and the Teachers' Sense of Self-Efficacy Scale and analyzed using analyses of covariance. Qualitative data were collected at multiple time points through observation, writing reflections, and focused group interviews and analyzed through qualitative coding. Findings revealed this type of low-cost, STEM professional development experiences can increase teachers' perceived self-efficacy in teaching STEM lessons and lay the foundation to increase collective teacher efficacy in teaching STEM lessons in a K-12 school community. Connections to existing research and STEM professional development are discussed. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]