This thesis comprises three original papers about learning rate of change in school mathematics. The overall aim of the thesis is to contribute with knowledge in this particular area of research. Within this aim, each of the original papers contribute with its own perspective. The theoretical framework used in the thesis is variation theory of learning (Marton & Booth, 1997; Marton, 2015), by which learning is seen as experiencing a phenomenon in a new way. This theoretical point of departure is reflected in the research question of the thesis: What is critical to discern to use and express rate as a measure of the relation of changes in two quantities? The empirical study was conducted as a learning study (Pang & Marton, 2003). A learning study is an iterative, interventional research arrangement in which teachers and researchers collaboratively explore a specific ability, the object of learning, worthwhile for the students to learn. The object of learning related to this thesis, ‘to express the quantitative rate of change of a linear relation’, was explored in a series of three research lessons at a secondary school. Data consists of students’ responses to written pre- and post-tests, and lesson videos. Some data have been analysed during the on-going empirical study and some data have been analysed after it was concluded. Principles from variation theory have been used as tools for analysis throughout the study. Main results of Paper I demonstrate how two critical aspects are identified and revised through the process of learning study. In Paper II the results indicate that qualitatively different questions in a task may affect students’ ways to relate changes in two quantities. The results of Paper III suggest how different perspectives of slope may promote homogeneity as an aspect of rate. Results also comprise six critical aspects of the object of learning, four of which was identified by revisiting the results of Paper II. In summary, the critical aspects also specify the meaning of a covariational perspective of rate. Results are discussed in relation to previous educational research about rate of change, covariation of quantities and students’ conceptions of rate and slope. Further research directions are suggested.

Syftet med denna studie är att jämföra olika frågeställningars betydelse för hur elever relaterar och uttrycker relationer mellan olika storheter i uppgifter om förändringstakt i matematik. Genom en kvalitativ analys jämför vi hur elever i årskurs 9 besvarar två olika typer av uppgifter om hur snabbt vätskevolymen i två medicinska droppåsar förändras. Analysen pekar bland annat på att en jämförande uppgift (”vilken förändras snabbast?”) kan öppna ett brett utfallsrum, där vi kunde observera fem kvalitativt skilda sätt att lösa uppgiften. Vidare verkar en uppgift som efterfrågar ett värde (”hur snabbt förändras den?”) kunna leda eleverna mot multiplikativa jämförelser, som ligger nära den vedertagna matematiska innebörden i begreppet förändringstakt. Avslutningsvis diskuterar vi de olika frågeställningarnas potential för att lyfta olika aspekter av begreppet förändringstakt och hur de skulle kunna användas av lärare för olika syften i undervisningen.