The role of number structures in pupils’ over-reliance on proportional methods

Previous research showed that primary school pupils over-use proportional methods especially when solving non-proportional missing-value word problems. The current study examines whether the numbers appearing in these word problems partly explain this phenomenon. In previous studies, the numbers in the problems formed integer ratios, which may have stimulated pupils to use proportional methods. A test containing proportional and non-proportional word problems was given to 508 4th, 5th and 6th graders. Numbers in these problems were experimentally manipulated so that the internal and external ratios were either integer or not. We found that in 4th grade, integer ratios elicited much more (inappropriate) proportional methods in pupils than non-integer ratios, while this effect was smaller in 5th grade and disappeared in 6th grade.