This article reports findings from a four-year formative experiment (Reinking & Bradley, 2008) investigating a summer writing institute for ninth graders entering an urban high school. Intended as enrichment, not remediation, for a heterogeneous group of students, and as a learning experience, not just a teaching opportunity, for practitioners, the institute was grounded in multiliteracies (New London Group, 1996) and scholarship on inclusive schooling (Udvari-Solner, 1997). Its essential elements included (1) composing by students in both print and digital genres, (2) a small set of instructional approaches effective for heterogeneous populations, and (3) co-teaching and co-planning by institute staff. This article focuses on teachers' efforts to support the writing development of English Language Learners (ELLs), who represented 20-30% of institute participants each year. Findings revealed that as teachers made adjustments to the institute model over time, their efforts to support ELLs' participation became more grounded in collective examination of varied student data. As teachers worked in community with each other (Swanson, 2007; Venter, 2004), they increased their ability to address student writers' diverse needs.