Chapter 4 Students’ Aggregate Reasoning with Covariation Keren Aridor and Dani Ben-Zvi Abstract Helping students interpret and evaluate the relations between two vari- ables is challenging. This chapter examines how students’ aggregate reasoning with covariation (ARwC) emerged while they modeled a real phenomenon and drew informal statistical inferences in an inquiry-based learning environment using TinkerPlots TM . We focus in this illustrative case study on the emergent ARwC of two fifth-graders (aged 11) involved in statistical data analysis and modelling activities and in growing samples investigations. We elucidate four aspects of the students’ articulations of ARwC as they explored the relations between two variables in a small real sample and constructed and improved a model of the predicted relations in the population. We finally discuss implications and limitations of the results. This article contributes to the study of young students’ aggregate reasoning and the role of models in developing such reasoning. Keywords Aggregate reasoning · Exploratory data analysis · Growing samples Informal statistical inference · Reasoning with covariation · Statistical modelling 4.1 Introduction The purpose of this chapter is to provide an initial scheme for understanding young students’ emergent articulations of aggregate reasoning with covariation (ARwC) in the context of informal statistical inference from growing data samples. Handling data from an aggregate point of view is a core aspect of statistical reasoning (Hancock et al. 1992). Predicting properties of the aggregate is the essential aspect of data analysis and statistical inference. To achieve this goal, one should develop a notion of data as an organizing structure that enables seeing the data as a whole (Bakker and Hoffmann K. Aridor (B ) · D. Ben-Zvi Faculty of Education, The University of Haifa, Haifa, Israel e-mail: kerenaridor@gmail.com D. Ben-Zvi e-mail: dbenzvi@univ.haifa.ac.il © Springer Nature Switzerland AG 2019 G. Burrill and D. Ben-Zvi (eds.), Topics and Trends in Current Statistics Education Research, ICME-13 Monographs, https://doi.org/10.1007/978-3-030-03472-6_4 71