The coherence principle states that all non-essential information in multimedia messages should be eliminated to minimise demands on cognitive resources. This assertion has been empirically verified in controlled laboratory studies with learners who have little prior knowledge and limited interest in the domain of instruction. It has not been investigated, however, whether the coherence principle generalises to real learning environments. In this study, 104 students from year 10, year 11, and first year university viewed either a concise or an extended online multimedia treatment on stellar spectra. The extended treatment included additional interesting information about the formation of black holes, galaxy collisions and the observation of dark matter. Following the multimedia, participants completed a retention and transfer test that covered only the material common to both treatments. Results showed students in both treatment groups achieved similar performance. This suggests that in authentic learning settings, interest may mitigate the effects of the coherence principle. Difficulties involved in measuring differences in learning within the constraints of a real learning environment are also addressed. (Contains 1 table and 3 figures.)