Research on teacher development indicates that student teachers appear to progress through developmental stages during their teacher preparation programmes (Conway and Clark (2003), Fuller (1969), Kagan (1992), Nias (1989), Pigge & Marso (1997). Supported by the Irish Research Council for the Humanities and Social Sciences, this three- year longitudinal research study builds on existing research by exploring and analysing comparatively the developmental trajectories of undergraduate and postgraduate teacher education students. Specifically, this paper aims to explore the following questions:1. What experiences do student teachers identify as formative in shaping their understanding of teaching?2. Do the self-selected formative learning experiences of undergraduate and postgraduate pre-service teachers point to a trajectory of teacher learning?3. Are there qualitative differences in the developmental trajectories of undergraduate and postgraduate teacher education students? The research is interpretative and uses a collective case study methodology. This paper details and analyses the ongoing reflections of six undergraduate and six postgraduate students during their teacher education programmes. The limited number of participants has allowed for considered and elaborated journal and interview data responses to emerge throughout the period of study. A range of within-methods tools including, reflective journals, e-mail communication with the author and interviews yield opportunities for analytical triangulation. The comparative, longitudinal and collaborative aspects of the research enhance validity. The journaling and interactive aspects of the research serve to challenge role, reflexive and ethical considerations and create a context for the rich qualities of qualitative research to emerge. This study yields significant and unique insights into the learning experiences which student teachers identify as formative in evolving their personal theories of teaching and learning; the existence, nature and characteristics of student teachers' trajectories of learning. the existence of qualitative differences in the evolution of the conceptualisations of teaching and pupil learning held by undergraduate and postgraduate student teachers;This paper contributes to the literature by presenting the trajectories of teacher learning employed by undergraduate and postgraduate students over a three-year period.Furthermore, the paper presents a methodology, developed in the course of this research, which can be used by teacher educators to enable student teachers to articulate, refine and modify their understandings of teaching and learning in an ongoing fashion throughout their teacher education programmes.As a consequence, the results of this study will have general implications for the design and delivery of teacher education programmes at National, European and International levels. Fuller (1969). F.F. Fuller, Concerns of teachers: A developmental characterization. American Educational Research Journal 6 (1969), pp. 207-226.Kagan (1992). D.M. Kagan, Professional growth among pre-service and beginning teachers. Review of Educational Research 62 2 (1992), pp. 129-169.Nias (1989). J. Nias, Teaching and the self. In: M. Holly and C. McMcLoughlin, Editors, Perspectives on teacher professional development, Falmer Press, London (1989).Pigge & Marso (1997). F.L. Pigge and R.N. Marso, A seven-year longitudinal multi-factor assessment of teaching concerns development through preparation and early years teaching. Teaching and Teacher Education 13 2 (1997), pp. 225-237