Research finds that student teachers often fail to make observable instructional goals, without which a secure bridge between instruction and assessment is precluded. This is one reason that recent reports state that teacher education needs to become better at helping student teachers to develop their thinking about and skills in assessing pupils' learning. Currently in Europe, the Lesson Study method and the Content Representation tool, which both have a specific focus on assessment, have started to address this problem. This article describes and discusses an intervention in which Lesson Study was used in combination with Content Representation in student teachers' field practice. Empirical materials from one group of student teachers were analyzed to illustrate how the student teachers worked with assessment during the planning of a lesson, how they implemented it in a research lesson, and how they used the gathered observations to make claims about assessment aims. The findings suggest that the student teachers placed greater emphasis on assessment through the intervention. However, it is also found that more attention should have been dedicated to the planning phase and that the group did not manage to keep a research focus throughout the Lesson Study process. This suggests that it properly would be beneficial with several planning sessions prior to the research lesson, as well as having an expert teacher leading the Lesson Study.