This study explored the extent to which an 18‐day history and writing curriculum intervention, taught over the course of one year, helped culturally and academically diverse adolescents achieve important disciplinary literacy learning in history. Teachers used a cognitive apprenticeship form of instruction for the integration of historical reading and writing strategies and content learning with the goal of improving students' historical argument writing. The intervention had positive and significant results for each writing outcome. After controlling for variables associated with students' incoming abilities, the researchers found moderate to large effects for all participants. Relative to basic readers in the control condition, those participating in the intervention scored higher in historical writing and writing quality and wrote longer essays; these results translate into effect sizes of .45 on basic readers' historical writing, .32 on their overall writing quality, and .60 on the length of their papers. Teachers implemented the reading and writing curriculum intervention with high levels of implementation fidelity, leading the researchers to explore additional factors that contributed to students' success after accounting for teacher effectiveness. The results indicate further benefits dependent on the degree to which students completed the curriculum.