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The effectiveness of an integrated
 STEM
 curriculum unit on middle school students' life science learning

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 post-assessment data of students' science learning outcomes for both the baseline group (taught via existing district-adopted 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 (POC) status. We conducted multiple regression analyses to explore the relationship between students' gender, POC status, and their learning outcomes. The results indicated that the intervention group students performed significantly better than the students in the baseline group. The repeated measures ANOVA showed that students in the intervention group retained science knowledge after 8 weeks of instruction. Finally, the regression analysis for the baseline group showed that gender and POC status were not significant predictors of their post-assessment scores. However, POC status was a significant predictor of post-assessment scores and knowledge retention for the intervention group. Overall, this study provides valuable findings on how an integrated STEM curriculum designed with engineering design and practices improves students' science learning outcomes.