Mathematical writing in school is difficult to teach. Reasons include that it is a domain in which there are rules for some parts of the writing like for example mathematical notation while others must be negotiated locally in the classroom. Writing is also seldom separated from the process of solving mathematical problems, creating a situation where students' texts rarely are assessed based on their communicational merits alone. Writing done in connection with problem solving also often fails to distinguish between writing as a cognitive tool and writing to communicate with others. In this article we present and discuss a teaching design that addresses these problems by creating a separation between problem solving and the production of formal written mathematical communication. This separation creates an opportunity for the communicational merits of the texts that students produce to be discussed in class using a framework that suggests qualities to be considered.