Teachers draw from many personal and professional experiences when organising and leading field trips. In order to identify the influences on teachers' field trip practices, I used surveys, interviews, artifacts and observations gathered from teachers who led trips to an aquarium. Findings clarified the types of influence and the impact that these influences had on practice. For example, teachers adapted knowledge acquired for use in their field trips from four types of training (1) informal mentoring, (2) past experience on various trips, (3) various outdoor education training and (4) traditional classroom education training. A focus was the nature of each of these training types and how teachers acquire and adapt their knowledge. Previous research has shown that, while a variety of cognitive and affective outcomes often results from field trips, there is also a pattern of underutilised resources and missed learning opportunities during trips. This study offers insight regarding strengths and weaknesses of teachers' preparation for leading field trips by documenting how and what skills are learned and applied. Therefore the findings presented here are suggestive of ways in which efforts to formally support and enhance teachers' trip-leading skills by means of professional development might build on teachers' existing sources of knowledge.