This dissertation explored transformative way of becoming a teacher in class teacher education. In this study, transformative learning was defined by Jack Mezirow and Robert Kegan as learning in which the learner’s meaning system – that consists of meanings and ways of making meaning – is transformed. In the context of teacher education, this means a change in the meanings that student teachers give to teaching, learning and education, and in the ways in which these meanings are constructed. The qualitative research was carried out in The Integrative Model of Teacher Education (CITE) at the University of Jyväskylä’s Department of Teacher Education. In CITE, learning is based on the principles of an explorative community in a long-term small group. The data was collected by observing students’ studies over two academic years and consists of field and research diaries as well as students’ study and research essays and other writings. Phenomenological and hermeneutic research methods were used in the data analysis. The phenomenological analysis focused on the general characteristics of the phenomenon of transformative way of becoming a teacher. The result of this analysis was a description of transformative way of becoming a teacher as a four-phase process. The phases are: 1. starting point, 2. crack, 3. ambivalence and 4. transformation. Hermeneutic analysis was used to examine and interpret how the transformative learning process occurred in practice for the subjects. For the first phase, the analysis focused on the students’ meaning systems related to teaching and learning at the beginning of the process and the starting point they set for the learning process. For the second phase the analysis focused on how CITE fragmented the students’ meaning systems and for the third phase the ambivalence that resulted from this crack was analyzed. Finally, for the fourth phase the transformative changes that occurred in students’ meaning systems were analyzed. The results of the study describe transformative way of becoming a teach-er as a long and ambivalent process that challenges discourses of educational policy that emphasize efficiency and speed. The findings can be used to inform the development of teacher education.