Abstract
This study investigated 1) the relation between proportional reasoning and comparison of intensive quantity (thickness), and 2) the effect of manipulation of juice and water believed to contain proportional reasoning on the comparison of thickness. Adjustment tasks (proportional reasoning) and comparison tasks (comparison of thickness) were individually administered to 160 pupils in grades 3, 4, and 5. Answers to the tasks and their justifications were analyzed. The results showed that 1) proportional reasoning was found in the 3rd and 4th grades when preceding a comparison of thickness; and that 2) manipulation involving proportional reasoning promoted the performance on thickness comparison tasks, especially in 4th graders. The factors promoting the performance and its process were discussed.
