Teamwork and collaboration skills are regarded as essential proficiencies in the current worlds of work, study and everyday life. A relevant question is whether and how pre-service teachers have opportunities to begin acquiring professional collaboration skills during their studies. In the current study, Finnish pre- and in-service teachers participating in a joint training programme were engaged in reflection tasks to evaluate their teamwork behaviour during a challenging pedagogical design task in mixed teams. The aim of this study was to examine how pre- and in-service teachers perceived their teamwork practices while performing authentic training activities together. The participants reflected on their own and their teams' behaviour in two ways: using a digital reflection survey tool repeatedly during the process and writing a reflection text. In the surveys, the participants scored both team behaviour and their own behaviour in the team relatively highly, but their own behaviour was evaluated as somewhat better than the overall team behaviour. In the reflective writing assignments, team behaviour was addressed more often than one's own behaviour. Experiences were mostly positive, but the participants also reported varying challenges. Based on the results, it can be suggested that to better guarantee the development of pre- and in-service teachers' collaboration skills, systematic guidance with adequate tools, is the requisite.