Contextualizing science instruction involves utilizing students' prior knowledge and everyday experiences as a catalyst for understanding challenging science concepts. This study of two middle school science classrooms examined how students utilized the contextualizing aspects of project-based instruction and its relationship to their science learning. Observations of focus students' participation during instruction were described in terms of a contextualizing score for their use of the project features to support their learning. Pre/posttests were administered and students' final artifacts were collected and evaluated. The results of these assessments were compared with students' contextualizing scores, demonstrating a strong positive correlation between them. These findings provide evidence to support claims of contextualizing instruction as a means to facilitate student learning, and point toward future consideration of this instructional method in broader research studies and the design of science learning environments. (Contains 6 tables, 3 figures, and 2 notes.)