Project Clarion, a Jacob K. Javits-funded project, focused on the scale-up of primary-grade science curricula. Curriculum units, based on an Integrated Curriculum Model (ICM), were developed for high-ability learners, but tried out with all students in Title I settings to study the efficacy of the units with all learners. The units focus on the development of students' conceptual understanding to undergird science content attainment. Teaching and learning models, such as concept formation and concept mapping were used to scaffold science learning and reasoning for appropriate curriculum differentiation. Science content mastery was measured using the Metropolitan Achievement Tests. Reasoning skills were measured using the Test of Critical Thinking. Understanding of macro-concepts and content attainment were measured by curriculum-embedded performance-based assessments. Students with the ICM outperformed students without the specialized curriculum in science content and reasoning skills, and showed greater growth in both conceptual understanding and content attainment.