Pre-service primary teachers mostly have negative attitudes towards science teaching and learning, and their science background is usually low. This usually results in them feeling unable or unconfident to teach science at school. A previous step to improve their willingness to teach science to children is that they feel they can learn in-depth any science core idea. To do that, a course conducted as oriented-research about a core science problem was developed and used to evaluate the influence of their previous science background and initial attitudes towards science teaching and learning on content knowledge attainment. The chosen science idea was about diurnal astronomy (Sun movements and the Sun/Earth model). Content knowledge attainment was assessed using learning indicators, which represent what pre-service teachers should "know" and "know how" on this science core idea. Overall, pre-service teachers achieved high learning levels on this topic, and no significant differences in content knowledge attained by students according to both initial attitudes and science background were found. This suggests that this teaching methodology could be useful for pre-service teachers to achieve a thorough knowledge on science core ideas, which is considered to be an important step to improve their willingness to teach science at the primary school.