Teaching outdoors has been established as an important pedagogical strategy; however, science classes rarely take place outside. Previous research has identified characteristics of teachers who have integrated out-of-classroom opportunities into their teaching repertoire; yet little is understood as to why teachers make these different pedagogical decisions. This paper explores the relationship between secondary science teachers' beliefs and their pedagogical practice during a two-year professional development programme associated with the "Thinking Beyond the Classroom" project. Using data from lesson observations, interviews, session questionnaires and field notes, six teacher case studies were developed from participants completing the programme. Data analysis reveals that teachers who successfully taught outside generally held social constructivist beliefs about learning and valued "authentic" science opportunities. Conversely, teachers who were less successful in teaching outside generally held traditional learning beliefs and simply valued the outdoors for the novelty and potential for fun. All the case study teachers were concerned about managing student learning outside, and for the majority, their concerns influenced their subsequent pedagogical practice. The findings are discussed in detail, as are the implications for pre-service and in-service professional development programmes related to outdoor science learning.