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Preparing preservice mathematics teachers (PSMTs) to make informed decisions and take action individually and collectively to address urgent sustainability challenges is the goal of education for sustainable development. Therefore, PSMTs’ literacy in interpreting data and graphing about the sustainability challenges available in the news and mass media is essential. Covariational reasoning allows PSMTs to create and interpret graphs as they envision two quantities that vary simultaneously. The present study aims to discuss how three preservice mathematics teachers’ covariational reasoning develops as they represent relationships between two quantities that vary in tandem. The study employed a case study method. The study subjects were three PSMTs from a private university in Yogyakarta, Indonesia. The PSMTs complete a digital task sequence during a teaching experiment. The digital task sequence was developed in Desmos. The digital task sequence facilitates the PSMTs to graph the relationship between the volume and height of water in various bottles. Their responses were analyzed using the Covariation Framework. The data analysis showed that the PSMTs’ covariational reasoning developed, progressing from the gross coordination of values to the chunky continuous variation level.

covariational reasoning; Desmos; graphing; preservice mathematics teachers; rate of change