The article examines student teachers' pedagogical language knowledge. The analysis is based on data from an applied task in which Finnish student teachers (n = 221) of 16 school subjects assessed second language (SL) learners' writing skills. First, we briefly discuss subject teachers' role in language and literacy teaching in the multilingual and multicultural classroom. Our findings indicate that the student teachers use a range of criteria but focus mainly on word-level assessment when assessing writing samples, and that their assessment orientation varies from technical to analytical. Finally, we discuss the challenges of developing teacher education to promote pedagogical language knowledge across the curriculum.