Fewer students in the United States are choosing to study and enter careers in the STEM disciplines-Science, Technology, Engineering, and Mathematics. This problem is being addressed through current educational reforms focusing on Integrated STEM curriculum and instructional design. This mixed-method quasi-experimental study researched the effects of science-engineering integration on student learning, student attitudes, and student interests in science within an elementary setting through the creation and implementation of an integrated science and engineering unit of instruction focused on the water cycle. Comparisons of student performance on end-of-unit science assessments revealed no significant differences in student learning between students who experienced an integrated unit of instruction and those who received an un-integrated science unit. However, increased student learning and interest in science was evidenced in responses to a student survey. Inasmuch as there is little in the way of frameworks to guide the legitimate integration of science and engineering instruction, this study offers a guide for teachers along with evidence of its efficacy.