The purpose of the present study was to compare the effectiveness of two instructional approaches in the acquisition of basic astronomy concepts. Sixty-three fifth-grade students were pre-tested on their knowledge of the shape of the Earth and the day/night cycle. Half of the students received standard, textbook-based instruction. The rest of the students received instruction that took preconceptions into account, and which focused on explanations that would maximise the plausibility of scientific conceptions. The results indicated that the experimental instruction had a strong positive effect on learning and understanding. In contrast, the standard instruction did not lead to significant pre-test/post-test gains.