The present study is one part of a larger research project dealing with the teaching and learning of mathematics in the latter part of the Swedish compulsory education and the first year of upper secondary school. The focus of the project as such is upon classroom communication with respect to teacher-student interaction on the one hand and students’ interpretation and understanding of the learning content on the other. The mathematical domain that is studied is algebra, and both mathematical concepts, which are new to the students, and concepts, which students are already familiar with, are of interest. It is frequently argued that algebra is an abstract and problematic area (e.g., Olteanu, 2007; Kieran, 1992; The Swedish National Agency for Education, 1999), which most students have not encountered in primary education in any formal sense, and which contains a body of new mathematical concepts. Thus, the teaching and learning of this particular area is an urgent domain for research on mathematics education.