This report summarizes the results of kindergarten through fifth grade students' academic achievement outcomes in mathematics and science following four years of campus-level participation in the Launching Elementary Academic Foundations (LEAF) to STEM program. The LEAF to STEM Program consists of three key components that were adapted for K-5 teachers from a secondary STEM curricular intervention within the same charter system. The three key components were: 1) an elementary-focused project-based learning STEM curriculum, 2) ongoing professional development for participating teachers, and 3) peer-to-peer mentoring with secondary STEM teachers serving as mentors to elementary STEM teachers. The charter school system in which LEAF to STEM was implemented is ethnically and racially diverse, with a higher percentage of students of color than the state in which the system operates (86.1% vs. 71.9% students of color). The system serves a high population of students identified as at-risk, including 60% of students identified as eligible for Free and Reduced Lunch and 24% of students identified as English Language Learners. At the time of randomization, the charter system had a total of 14,572 grades K-5 students on 34 K-5 campuses. The cluster randomized-controlled trial assigned thirty-two K-5 campuses within a large charter system to a treatment/control (business-as-usual) condition using stratified sampling. Campuses were stratified into four groups based on whether a campus's total percentage of students classified as eligible for free-and-reduced price lunch (FRL) fell above or below the system-wide average percentage of FRL students. Within each of those levels, schools were further stratified into two additional groups, based on whether the percentage of a school's students meeting NWEA MAP Reading and Mathematics growth targets in the year prior to randomization to treatment was above or below the system-wide average. Student achievement in mathematics and science was measured using the NWEA MAP Rausch Interval Unit (RIT) scores for mathematics and science for all grades K through five students enrolled in campuses at the time of randomization. Mathematics baseline RIT scores, as well as RIT scores for years one (spring 2020), two (spring 2021), three (spring 2022), and four (spring 2023) of treatment were available for all students, whereas science RIT scores were only available for grades 4 and 5 students after one year (for both 4th and 5th grade students at the onset of the program) or two years of treatment (for 4th grade students only at the onset). Two-level hierarchical linear modeling (students nested in campuses) was employed to explore the impact of treatment on students' mathematics and science achievement (NWEA MAP scores) controlling for demographic background (i.e., ethnicity and gender) and prior achievement at the onset of the LEAF to STEM (beginning of year 1). Results indicated no statistically significant differences in mathematics and science achievement between students in the treatment and control conditions after four years of the exposure to the LEAF to STEM program. When broken down by the grade level, results still did not indicate any significant differences between treatment and control groups in mathematics and science achievement.