Content area educators seeking to integrate genre-based writing instruction into their teaching are faced with the task of negotiating the simultaneously constraining and creative aspects of genres, in relation to their content-area teaching and also in relation to various needs and levels of proficiency among students in diverse classroom settings. To explore how this negotiation plays out in instructional practice, this case study, set in a Swedish grade-eight diverse classroom, documents a genre-based history unit where students were offered a range of genres for writing. This multi-genre design offered students a range of genres and choices for their writing. It was found that the teacher could simultaneously present these various genres as flexible and fixed entities, without this alternation posing a problem for students. When scaffolding students’ writing, the teacher was found to guide students either by offering them correct (limited) choices, or wise (open) choices with the overall purpose of steering students towards history-curriculum assessable texts, while still allowing room for creativity for more able students. These findings have implications for how we can understand and address issues related to genre-based instructional practices.