As pointed out by Seymour Papert, teaching teachers might be more complex and difficult than otherforms of adult learning. In Sweden, as in many other countries, the introduction of computerprogramming in compulsory education is an ongoing process that involves teacher professionaldevelopment. Results from the first generation of teacher training in fundamental programmingindicates that motivation and high pass rates are not always the case. The aim of the study is toanalyse and discuss success factors and lessons learnt in teacher professional development.This study was conducted with a case study approach, with data collected from various data sources.All the courses where data have been gathered are part of a nation-wide training program formathematics and technology teachers in K-12 education. The data triangulation and themethodological triangulation were built around course evaluations, group discussions with courseparticipants, and a survey directed to the subject matter experts of the teacher training courses. Athematic analysis was filtered through the theoretical assumptions of communities of practise andadult learning.Four interesting main findings are, 1) the relevance of study groups, 2) course participants’appreciations of concrete workshop sessions, 3) teachers’ perception of a two-folded time trouble, and4) teachers’ expectations of reusable takeaways from the course. Finally, the recommendation is tofree more time for teachers to participate in collaborative hands-on activities and collegial reflection.