The inclusion of "nature of science" (NOS) in science education has for a long time been regarded as a crucial component in the teaching for scientific literacy. The aim of this study is to investigate how in-service science teachers plan, implement, and afterwards reflect on a NOS teaching session. The participants in the study are Swedish in-service science teachers (n=4) in grades 4-9. Sources of data are teacher-group discussions (before and after the NOS-session), classroom observations, and teachers’ reflective notes. The analytical framework used in this study is developed with a point of departure in the NOS tenets described by Lederman (2007). The preliminary results indicate that although the teachers in different ways explicitly address many different aspects of NOS during the teaching sessions, and they believe that their students are interested in the provided tasks, the teachers themselves are having a hard time coping with the clash between the implemented NOS-session and more traditional views of science teaching.