Recent reforms in education call for science teachers to incorporate STEM concepts into their curricula. This study explores the association among student and teacher demographics, and student learning of engineering content and attitudes towards STEM after participation in an elementary or middle school engineering-based science curricula. Analysis of 732 students' scores on engineering content knowledge assessment and STEM learning attitudes survey revealed several significant factors that influence students' post-survey and assessment scores. Our analysis identified English language learner (ELL) status and special education (SPED) status as significant predictors for post-test scores at the elementary school level. At the middle school level, SPED status and ethnicity were found to have significant effects for students' post-test scores. Student gender was found to be a significant predictor of student attitudes after taking the curriculum. Additionally, students who were taught by teachers that participated in two consecutive years of STEM professional development (PD) program had more positive attitudes towards engineering compared to students taught by teachers attending the PD program for only 1 year. These results suggest the ability of design-based science curricula to close the achievement and attitudinal gaps towards STEM in some student demographics. Additionally, our data revealed that continued PD can have positive effects on student attitudinal outcomes, suggesting long-term PD as an avenue to improve science education.