Abstract
Promoting the concept of density is regarded typically as the domain of science teachers. However, density as the relationship between an object's mass and volume highlights the importance of foundational measurement concepts located in the mathematics curriculum. As an intensive relationship, understanding density also requires a degree of proportional reasoning, but research has repeatedly shown that students' understanding of proportion and proportional thinking is generally poor. An instructional sequence for density was developed and iteratively implemented in several middle school (fifth grade to eighth grade) classrooms using a design research approach. This paper presents an outline of the unit sequence and highlights key points within it where particular mathematics knowledge and understanding was required. The capacity of this unit for promoting proportional reasoning is discussed. In this paper, the unit sequence is further analysed through the lens of numeracy. In this analysis, a rich model of numeracy is used to consider the potential of this unit for promoting numeracy, and to draw implications for teaching of density in science with respect to consideration of the numeracy demands of this difficult topic.