Students' abilities to master the genres of science must include not only factual knowledge. They also have to negotiate what they want to achieve with their texts and their ideas about writing and themselves as writers and science students. In this article, classroom observations, text analysis and interviews are combined in a case study of two students' experimental reports in order to investigate the relationships between identity, action and meaning-making. The students show important differences in their relations to school science and teacher expectations in terms of familiarity with the experimental report genre and identity. Being able to interpret and discuss with students what they are 'up to' in their texts is important for teachers in order to improve students' reflections on their writing practices as well as in order to make norms and assumptions underlying teaching practices explicit. This will help students to negotiate and request meaningful relations to science.