Recent calls for reform in K-12 science education and the National Academy of Engineering's Grand Challenges for Engineering in the 21st Century emphasize improving science teaching, students' engagement, and learning. In this study, we designed and implemented a curriculum unit for sixth-grade students (i = 1305). The curriculum unit integrated science and engineering content and practices to teach ecology, water pollution, and engineering design. We investigated the designed integrated STEM unit's effectiveness in students' science learning outcomes on pre-, post-, and delayed post-assessments. We collected pre-and postassessment data of students' science learning outcomes for both the baseline group (taught via existing districtadopted curriculum) and an intervention group (taught with integrated life science and engineering curriculum). We used a quasi-experimental research design and examined differences between baseline and intervention groups. We used ANCOVA to explore differences in students' learning in baseline and intervention groups. Furthermore, for students in the intervention group, we conducted repeated-measures ANOVA to investigate knowledge retention. Our analyses also accounted for students' gender and People of Color