601 © Springer International Publishing AG 2017 G.A. Stillman et al. (eds.), Mathematical Modelling and Applications, International Perspectives on the Teaching and Learning of Mathematical Modelling, https://doi.org/10.1007/978-3-319-62968-1_50 Chapter 50 Assessing Mathematizing Competences Through Multiple-Choice Tasks: Using Students’ Response Processes to Investigate Task Validity Brikena Djepaxhija, Pauline Vos, and Anne Berit Fuglestad Abstract In this chapter, we report on multiple-choice tasks for assessing mathe- matizing competences of grade 9 students. The task format is complex, consisting of two layers. In the frst layer, students are asked to consider a holistic modelling problem. In the second layer, they are asked for an atomistic competence (making assumptions, assigning variables, etc.) related to the same modelling problem. We conducted a qualitative study to investigate the validity of these tasks based on stu- dents’ response processes. Eight students worked in pairs solving the tasks collab- oratively. The results show that all students were able to handle the layered task format. They refected meta-cognitively on the holistic modelling problem, but none of them started solving it in itself. All students considered the remainder of the task, which made them focus on a specifc mathematizing activity. Keywords Assessment • Holistic assessment • Mathematizing • Lower secondary students • Multiple-choice tasks • Task format • Task validity • Validity based on response processes 50.1 Introduction Assessment is an inseparable part of education. Assessment is needed for reporting students’ learning outcomes to parents, policy makers, teachers, school leaders and students themselves. Also, assessment is used in educational research. For the B. Djepaxhija (*) • P. Vos • A.B. Fuglestad Department of Mathematical Sciences, University of Agder, Gimlemoen 25, 4604 Kristiansand, Norway e-mail: brikena.djepaxhija@uia.no; fpvos@hotmail.com; anne.b.fuglestad@uia.no