Informed by curriculum theory, this in-depth qualitative case study examined the experiences of one senior teacher, Stephen, as he enacted the first unit of Queensland's new "Earth and Environmental Science" (EES) syllabus. This study aimed to understand how Stephen navigated the 'space' between the intended and enacted curriculum, by focussing on what informed his teaching practice, and how Education for Sustainable Development (ESD) was realised (or otherwise). The realisation of ESD was limited to a few instances of teaching students about sustainability content, as Stephen's attention was turned to issues of time and student assessment, following major curricular reform. The tensions that Stephen recounted appeared to relate to a narrowed space between the intended and enacted curriculum, which manifested in feelings of reduced teacher autonomy. The implications of these findings for realising ESD in the context of curricular reform, and the importance of teacher reflexivity in achieving ESD, are discussed.