Around the world, programs have been developed for science teachers’ work on literacy in multilingual settings with the assumption that science teachers need an understanding and a repertoire to move between daily and scientific discourses. This poster presentation reports from a project which aims to gain a better understanding of the development of literacy in science teaching through the study of meaning construction in multilingual secondary classrooms in which teacher, students and texts interact. To that end, leading experts in the field of text analyses, science pedagogy, second language learning and educational linguistics, join their forces in a double case study. These different perspectives on scientific literacy are starting point for small-scale interventions that analyses the interaction of teacher, student and task characteristics. Data is generated through mixed-method approach and include video recording of teachers planning meetings and classroom practice (whole class and student group work) along with questionnaires. Furthermore is students’ written work collected and interviews with teachers and focus group interviews with students. The quantitative data comprises of multiple-choice tests where three types of words chosen from students’ textbooks are probed: science concepts, homonyms and general academic words. The preliminary results indicate that time spent in the Swedish school system is decisive; it is almost a linear correlation between results on word tests and the time the students have learned Swedish. Furthermore, it seems that the general academic words raise the greatest challenges. The analysis of the teachers’ professional development make use of the interconnected model for professional growth (Clarke & Hollingsworth, 2002) and the results indicate that although the teachers had extensive experience in teaching multilingual students they broaden their competence with new insights an teaching strategies.