This article presents the main results of a case study on teachers' professional development in terms of competence and identity. The teachers involved in the study are allocated time by their schools to participate in professional "affinity group" meetings. During these meetings, the teachers gather and analyse school-based data about factors which persistently create and sustain challenges in effective student education (grade K-10). This process improves their understanding and undertaking of job-related tasks. The affinity group meetings also influence the teachers' professional identity. The research findings thus illustrate the fact that the analytical approach of affinity groups, based on the analysis of the difficulties in their daily job, provides good results in terms of competencies and identity perception. In general, as a result of meeting in affinity groups, adult learners develop professional competencies and identities which are considered crucial in rapidly changing schools characterised by an increased focus on, among other things, lifelong learning, social inclusion, school digitalisation, and information literacy. The research findings are thus relevant for ministries and school owners, teacher-trainers and supervisors, schools and other educational institutions, as well as teachers and their organisations worldwide.