This study examines Finnish and English primary student teachers' ideas when planning to teach a physics topic during their science education studies. Many primary student teachers lack sufficient subject knowledge, which prevents them from constructing the scientific pedagogical content knowledge that enables them to concentrate on pupils' thinking and process skills needed in a physics topic. Therefore they will have problems constructing learning environments that encourage pupils to take active control of their learning. In order to develop effective pedagogical content knowledge it is of the utmost importance that the science educators responsible for physics courses pay special attention to the promotion of favourable attitudes towards the teaching of physics topics. This can be done by focusing on how to teach some basic familiar topics. Quality, not quantity, is important in focusing on both subject knowledge and pedagogical content knowledge. The construction of pedagogical content knowledge is a complex interrelationship of attitudes, subject, and pedagogical knowledge. All three of them need to be developed to enable students to confidently and effectively teach young children.