This study researched the use of writing-to-learn strategies within a high-school (Year 11) chemistry classroom. The writing task itself asked the students to write a business letter to a younger audience of middle-school (Year 7) students. A mixed-method design was used for the study, incorporating pre/post- testing with semi-structured interviews. The evidence supports that the treatment students performed statistically significantly better on a conceptual question compared to the control group. Additionally, the treatment students felt that writing to a younger audience prompted them to use different language than they would have if, for example, writing to their teacher. Further, the treatment students described that the writing task promoted their understanding of and their confidence in their knowledge of the stoichiometry concepts addressed in class.