This study explored disciplinary writing in grades 4-6 and the potential of writing to learn and learning to write across the curriculum to prepare the pupils for their future writing. Using Ivanic's discourses of writing as an analytical framework, observation protocols from 104 observers in 374 lessons in 76 Swedish schools were analyzed exploring school writing in the different curriculum subjects. Analysis of the data reveals that in most lessons the teachers required their pupils to write with a single focus on reinforcing learning, enacting three of Ivanic's seven discourses of writing: "thinking and learning" discourse, "skills" discourse, and "social practices" discourse. Much less frequently overall but commonly in language lessons, teachers required their pupils to write with a dual focus, developing writing proficiency while reinforcing learning. In these cases, all of Ivanic's discourses were enacted. The results suggest potential for a dual focus on writing to learn and learning to write to further develop the pupils' writing across the curriculum.