This paper reports a qualitative case study of a collaborative project between an ESL researcher and a history teacher teaching in a late immersion school in Hong Kong. The project aims to help a Grade 9 class to write history essays on their own instead of copying from the textbook, which is a common phenomenon in Hong Kong schools. The researcher and the history teacher collaborated on the design and teaching of four writing activities during a semester. The design of the writing activities was guided by a pedagogical framework for integrating content-language learning in late immersion, where content learning is increasingly complex and abstract and the language use is correspondingly more complex and specialized. The project was successful in helping students to write on their own and in improving that writing, particularly in terms of text structure. A major contribution to this success was the collaboration between a content specialist and a language specialist. Challenges faced in the collaboration between the content and language specialists and future directions for collaboration are shared.