The issue of this paper is to discuss the significance of the iterative process, characteristic for Lesson and Learning Studies, related to the knowing students need to develop in order to master a specific learning object. A characteristic aspect of learning studies as a research method, as developed by Marton & Pang (2006), is the use of a learning theory. The research issue is often related to learning outcomes and/or the development of learning theory used. My concern is rather what kind of subject specific knowledge, related to a specific learning object, it is possible to develop, and the importance of the iterative process of the model? The paper is related to a Learning Study in mathematics (subtraction), in a Swedish school. In the study, two cycles of a lesson where conducted with children aged 10-11 years. The repeated analyses from these lessons resulted in teachers deepening their understanding of the kinds of problems the students where struggling with. Comparisons between teaching, the content, and the students’ answers during the first and the second lesson, resulted e.g. in the teachers realizing that they had to introduce negative numbers much earlier than what is recommended in Swedish textbooks.