The focus of this article is on relations between classroom interaction, curricular knowledge and student engagement in diverse classrooms. It is based on a study with ethnographic perspective in which two primary school classes in Sweden were followed for three years. The analysis draws on Halliday's Systemic Functional Linguistics. The results indicate that language use in the classrooms is on a basic everyday level and that high teacher control results in low-demanding tasks and low engagement among students. Interaction in the classrooms mainly consists of short talk-turns with fragmented language, frequent repairs and interruptions, while writing and reading consists of single words and short sentences. Although the classroom atmosphere is friendly and inclusive, second language students are denied necessary opportunities to develop curricular knowledge and Swedish at the advanced level, which they will need higher up in the school system. The restricted curriculum that these students are offered in school thus restricts their opportunities to school success. Thus, I argue for a more reflective and critical approach regarding language use in classrooms.