RUME 28
2026
Alexandria, Virginia
Multiplying Fractions With Sunlight: A Scaling Model
Page: 1422
Physical models are frequently used in elementary mathematics classrooms to support students’ understanding of multiplication. These models are discrete, and many represent multiplication as repeated addition, area or an array. Thompson and Saldanha (2003, p. 104) found that “thinking about multiplication as repeated addition leads to severe difficulties in later grades” and Hurst (2015, p. 11) suggested that “multiplication as scaling…is a key aspect of thinking that needs to be developed.” McLoughlin and Droujkova (2013) developed a diagrammatic definition of multiplication using parallel lines to scale the length of one segment by the length of a different segment. We developed the SunRule, an interactive device that harnesses parallel rays of the sun to perform multiplication. Beams of light cast shadows from gnomons onto a measuring plane; by varying the tilt and height different multipliers, multiplicands, and products can be generated.