This study examined the impact of an Adapted Lesson Study Project (ALSP), an undergraduate course assignment, utilized for field-experience, on teaching efficacy, and the quality of lessons developed by pre-service teachers. Participants consisted of 23 undergraduate early childhood education students enrolled in an early childhood mathematics and science education course. The study used a mixed-methods model. Results of a paired samples t-test on the Sense of Teaching efficacy survey indicated significant differences in the sub-categories of instructional strategies and student engagement from pre- to post-participation in the ALSP. Lesson plans were quantitatively evaluated using a rubric developed to assess lesson quality. Lesson observation, reflection, and revision notes were analyzed using content analysis. Results indicated the ALSP, which included iterative collaborative and reflective practices, improved teaching efficacy and the quality of lessons. The study provides a viable methodology for the inclusion of Lesson Study processes within short-term field-based projects in teacher preparation programs. (author abstract)