Despite the research evidence on the effectiveness of collaborative learning (CL), the implementation of this teaching strategy has not yet found a profound place in teaching practice. As a consequence, several studies have investigated teachers' motives regarding and experiences with the use of CL. Most of these studies concern however senior teachers, whereas new generations of teachers are important actors in the process of educational innovation. Hence, it is crucial to explore novice teachers' stories about CL implementation: what motivates them to implement this teaching strategy, what hinders them and how do they handle the challenges they are confronted with? The answers to these questions may provide useful information for improving the teacher education curriculum regarding CL. In this respect, the present study intends to study pre-service and beginning teachers' experiences with CL in classroom practice, after a formal training pertaining to CL as part of their teacher education programme. The aim is to identify the main challenges student and novice teachers encounter when they want to implement CL in their teaching practice, and how they position themselves in these challenges. A qualitative case study design with in-depth interviews in the Flemish context (Belgium) was used to gain access to the particular experiences of each teacher, and to the processes of interpretation and meaning-making that go with those experiences. Participants were interviewed individually one week before graduation (n?=?15). After at least half a year of experience in the teaching profession, 10 participants were interviewed for a second time. In the present study, we present the results from a cross-case analysis, using the method of constant comparative analysis to identify similarities or differences, and to capture recurring patterns within the data. The findings reveal several dilemmas that illustrate the conflicting options teachers are facing in relation to their colleagues, their pupils, the curriculum and in the classroom context when they intend to implement CL. In particular, the following dilemmas were identified: two dilemmas related to professional autonomy (student teachers: teacher autonomy vs. pre-service performance assessment; novice teachers: teacher autonomy vs. institutional conformity), further dilemmas related to teachers' beliefs about pupils' readiness for CL vs. evidence about pupils' readiness for CL, investing in innovation vs. curriculum and job pressure, and pedagogical intentions vs. contextual constraints. In most conflicting situations, student and novice teachers position themselves in the challenge by opting for non-implementation.