Proportional Reasoning
Proportional reasoning has been emphasized. NCTM (2000) suggested that proportionality is an “integrative thread that connects many of the mathematics topics.” (p. 217). Inhelder and Piaget (1958) identified proportionality within Piaget’s stage of formal operational reasoning and illustrated it as ability to aware a secondary relationship between two pairs of quantities. Lamon (2007) proposed that proportional reasoning occurs when students recognize co-variation of quantities and in-variation of ratio simultaneously. It was reported that students use different strategies according to the types of given proportion problems. For example, Cramer, Post and Currier (1993) found that students made use of several strategies such as unit-rate, factor-of-change, fraction, and cross-product algorithm in solving proportional problems categorized as a missing value, numerical comparison, and two types of qualitative situations. This implies that the use of diverse proportional situations is helpful to analyse students’ proportional reasoning ability.
However, it is not easy for students to figure out how to solve various proportional problems. Students often use additive reasoning in solving tasks where proportional reasoning is required (Singh, 2000), or non-constructive strategies without reasoning such as avoiding, visual or additive approaches and pattern building (Lamon, 2007). These difficulties result from the lack of profound understanding of multiplicative relationship between quantities, which is the foundation of proportional reasoning. Given this, it seems important to explore the relationship between multiplicative thinking and proportional reasoning.