Teacher education for sustainability is a central part of integrating sustainability into classrooms and schools. However, educating for sustainability is not limited to increased content knowledge; rather it encompasses different forms of knowledge that embrace the normative, dynamic and action-oriented nature of sustainability. Curriculum for a summer sustainability programme had previously been developed based on an interdisciplinary approach which incorporates research and practice from the fields of education pedagogy, sustainability and behaviour change. This article synthesises the insights provided by K-12 teachers who participated in this programme and another teacher who utilised the curriculum during a sustainability unit in her 8th form science class in Phoenix, AZ. Data was collected through surveys and interviews over the course of a year. The key findings indicate that one of the major barriers to moving away from traditional, didactic approaches to education is the importance placed on standardised tests. As long as external forces and incentive structures reinforce methods of lecture and assess, teachers will struggle transitioning to more experiential, real-world methods that enhance a multiplicity of knowledge. One important suggestion made by the teachers was for increased support by universities through pre-service and in-service programmes focused on educating for sustainability.