This paper is a report of the Australian segment of an international multi-campus project centred on improving understanding of the Moon’s phases for preservice teachers. Instructional strategies adopted for a science education subject enabled Australian participants to make extended observations of the Moon’s phases and keep observational data records which were shared in asynchronous on-line discussion with fellow preservice teachers in the USA. An adaptation of an online inventory of lunar phases was completed by participants before and after the observation cycle. The analysis of inventory data showed that although there was statistically significant overall improvement in mean scores for the inventory this could be accounted for by statistically significant increases in only some conceptual domains related to the lunar phases. In addition, the findings indicate that some concepts involved in having a deep understanding of lunar phases can be improved by instruction however, misunderstandings of other concepts involved in lunar phases are difficult to change and may require increased attention to developing students’ visual-spatial capabilities.