“…The increasing research focus on equity and access for all learners (Secada, 1992;DIME, 2007) has added a third function, language as unequally distributed learning prerequisite, since limited language proficiency in the language of instruction can constrain the mathematical learning opportunities in mathematics classrooms (Snow & Uccelli, 2009). This does not only apply to students whose family language differs from the language of instruction (students with minority languages or immigrant status, Haag, Heppt, Stanat, Kuhl, & Pant, 2013;OECD, 2007;Barwell et al, 2016) but also for monolingual students with under-privileged socioeconomic status (Heinze, Reiss, Rudolph-Albert, Herwartz-Emden & Braun, 2009;Prediger, Wilhelm, Büchter, Benholz, & Gürsoy, 2015). That is why monolingual and multilingual students with low language proficiency in the language of instruction are subsumed under the unifying construct "language learners" in this volume (cf.…”