It is well known that many primary teachers have a negative attitude towards science as well as limited science subject matter knowledge. During a course, 40 primary science student teachers were video recorded to follow their activities during practical experiments in physics. After every workshop, they watched the video in order to reflect on their activities and communication in the group. After the course a questionnaire including a storyline was used to elicit the student teachers´ perceptions of their development of subject matter knowledge during the course. Finally, five participants were interviewed. The results give an insight into factors that primary student teachers described as important to develop subject matter knowledge and a more positive attitude towards physics.