Educative curriculum materials present a promising mechanism for promoting more ambitious science teaching in elementary classrooms, including engaging students in science practices. Integrating science practices with science content is emphasized in new education reforms. Elementary teachers, however, face challenges in engaging children in science practices such as scientific argumentation. We propose that the justification of predictions could serve as an entrée to scientific argumentation in elementary grades. To support elementary teachers in integrating science content with science practice, including justifying predictions about scientific phenomena, we added educative features to 2 existing upper elementary inquiry science units, 1 on electric circuits and 1 on ecosystems. This article reports results from a large-scale, quasi-experimental study with 2 conditions: the treatment condition, in which teachers had educative features, and the comparison condition, in which teachers had the original curriculum materials. This study sought to characterize differences in students' written predictions with justification across condition and discipline. In the treatment condition, in which teachers were using the educative curriculum materials, the students' predictions with justification showed significantly greater improvement in quality scores from the preunit assessment to the postunit assessment compared to the comparison condition. In addition, there was more evidence of teacher support for justifying predictions in the collected notebooks and enactments in the treatment condition compared to the comparison condition. These findings have implications for curriculum developers and teacher educators, suggesting an important role for educative curriculum materials in promoting reforms in science education.