Introduction The literature into students’ understandings of science is substantial (as illustrated by the extensive bibliography by Duit, 2005). A significant finding of many research studies has been that students’ ideas of the world are often formed before any formal instruction and are often quite different from scientifically accepted ideas. In addition, many studies have found that students’ non-scientific ideas are particularly resistant to change, or they change in unexpected ways, within the formal setting of the classroom. What is advocated to address these research findings are constructivist teaching and learning strategies (Hubber & Tytler, 2004). Such strategies are informed by the learning theory of constructivism, which recognises that learners construct, rather than absorb, new ideas within the context of their personal knowledge, and they actively generate meaning from experience. Learning is viewed as conceptual change produced by the construction and acceptance of new ideas or the restructuring of existing ideas of the learner. Constructivist teaching approaches to the process of learning are viewed as activities that explicitly aim to help students to make the constructions that lead to a conceptual understanding of the scientific points of view (Treagust, Duit & Fraser, 1996). Within such approaches students are active learners who come to the classroom with prior notions of natural phenomena that they use to make sense of their everyday experiences (Laverty & McGarvey, 1991). As students actively make sense of the world by constructing and reconstructing their own viable meanings (von Glaserfeld, 1989), constructivist teaching approaches then become a matter of creating situations in which students actively participate in activities that enable them to make their own viable explanations of their sensory experiences (Wood, 1995). Given that the research literature has found that students from different countries and cultures have been found to hold similar alternative conceptions (Tytler, 2004) then it may be argued that constructivist teaching and learning strategies are advocated for all students. However, it is not clear what opportunities and dilemmas constructivist approaches to the teaching and learning of science presents in classrooms of students who are taught in a language other than their own native language. The following sections of this paper describe some of the author’s research in adopting constructivist teaching and learning strategies in the teaching of optics to Year 10 (Hubber, 2002, 2005a, 2005b). While the students in this research were English speaking and taught in English this paper will discuss the applicability of employing constructivist teaching and learning approaches to English as Second Language (ESL) students.