To address the confusion resulting from difficulties with proportional reasoning among preservice physical science students, a cube-assembly activity was used to bring a sense of concreteness to abstract ideas. The activity took students from the concrete step of assembling cubes of various sizes and directly measuring their properties to slightly larger cubes, to significantly larger cubes. Then, in the analysis of the table, students carried out the calculations of several ratios that showed how the density of the material did not change regardless of the change of mass and volume of the material, and some mathematical formalism was built based on the empirical data generated in the activity.