This study investigated the influence of a short explicit-reflective Nature of Science Course (NOSC) on access students' ideas about the Nature of Science (NOS). Eighty five students registered for a Bachelor of Science degree at the University of the Western Cape in South Africa went through a seven week course that deliberately sought to develop students' NOS ideas through history of science contexts. Fifty students (30 males and 20 females) completed pre- and post-intervention questionnaires assessing their cognitive and epistemic NOS understandings. Six students were interviewed. The results show that as a result of the course, students' NOS understandings shifted decisively from naïve to being reasonably informed. However, many students showed resistance to changing some of their NOS views, for example, on the issue of 'proof' in science. The course was found to have more impact on students' cognitive ideas than on their epistemic views. From the results, it appears that the effectiveness of using history of science to teach about NOS is affected by students' understanding of related science content. It is recommended that explicit NOS teaching must negate the 'confounding influences' operating on a student's conceptual ecological system.