Primary school teachers face the challenge of supporting the academic vocabulary development of pupils with widely ranging linguistic, social and cultural backgrounds, and thus need specific knowledge of the role of vocabulary in literacy development and of methods that stimulate vocabulary growth. This presentation introduces a Swedish research project aiming to describe and explain the variation in vocabulary growth in pupils attending a multilingual primary school with many newly arrived pupils. The two-year project begins with a series of tests assessing the vocabulary depth and breadth of 2nd and 5th grade pupils. After analyzing results and conducting classroom observations of teachers’ work with vocabulary, the next step is organizing workshops where teaching staff and researchers discuss literature on vocabulary instruction and devise new classroom approaches. Results of these first-year activities will be presented, highlighting pupils’ vocabulary development in relation to age, gender, language background, as well as number of years in Sweden. Final results, including follow-up testing during the second year, can inform the work of both teachers and researchers.