In this paper, we present a professional development/upgrading programme in science for early-years teachers and investigate its impact on the teachers' competencies in relation to their knowledge and teaching of science. The basic idea of the programme was to motivate the teachers by making them members of an action research group aimed at developing and implementing curriculum activities to which they would contribute and thus meaningfully engaging them in their own learning. The programme used a 'collaborative partnership' model for the development of the activities. In this model, the collaborative notion is defined as an act of 'shared creation': partners share a goal and members bring their expertise to the partnership. Within this context, the partners were a researcher in science education with a background in physics, who also served as a facilitator, and six in-service early-years teachers with a background in early-years pedagogy and developmental sciences, who had many years of experience (classroom experts). These teachers participated in the programme as co-designers, but were involved to a significantly lesser degree than the researcher. The programme procedures comprised group work and individual teachers' class work. Data sources included teachers' essays, field-notes, lesson recordings and group-work records. Data were qualitatively analysed. The main results indicate improvement of teachers' 'transformed' knowledge of the subject matter, development/improvement of knowledge of instructional strategies, including factors related to quality of implementation of the activities, knowledge of the pupils and improvement of the teachers' efficacy.