Creating congruent links between the three representations of science understanding - macroscopic, microscopic, and symbolic (Johnstone, 1991), is important for the conceptual understanding of pressure and Boyle’s Law. Twenty-one grade 11 chemistry students participated in a science program that culminated in students scuba diving. Students recorded their initial conceptions throughout the four-and-a half week teaching intervention and completed assignments using Johnstone’s three representations as the basis for their responses. A two-tier multiple choice diagnostic was developed to assess student conceptions of pressure and Boyle’s Law at the end of the teaching intervention. Results of this study suggest that these methods were helpful in promoting conceptual change. The structured sampling of student conceptions throughout the intervention provided information about the following: (a) similarities in student naïve conceptions; (b) changes in student conceptions; (c) the presence of tenacious, alternate conceptions; and (d) teaching strategies, lesson sequences, and demonstrations that appeared to be effective in promoting scientific understanding of pressure and Boyle’s Law.