It is generally agreed that it is difficult for schools to bring about lasting changes in classroom practice. This paper gives an account of an action research group of 21 practitioners in an upper secondary school in Iceland, where a new model, the Change Room, was introduced to enhance changes in classroom practice. The aim was to increase students' sense of responsibility for their studies. The Change Room connected the Change Laboratory, one of the methods of developmental work research established by Engeström and action research as elaborated by McNiff. In the Change Room the activity theory provided the teachers with a conceptual framework and tools to analyse what changes were needed and wanted in classroom practice and action research provided an approach to guide them when carrying out and evaluating these changes. Change Room meeting records were used for reflection, which revealed that the main tensions teachers experienced in classroom practice was firstly between didactic and dialogic teaching methods, secondly between the demand to cover the syllabus and a sense of urgency for deep learning and thirdly between active and passive students as learners. In order to resolve these tensions teachers tried out new methods to attempt to change their practice in the direction of more active student learning and more listening to students' voices. The Change Room offers a promising direction to increase teachers' agency to change their practice and sustain that change. As such, it speaks to international concerns about effective school reform.