The key competencies as a curriculum construct have appeared in several national curricula from the early 2000s. Many have their origins in the Definition and Selection of Key Competencies Project (DeSeCo), commissioned by the supra-national Organisation for Economic Co-operation and Development (OECD). A number of international critiques have highlighted tensions between neoliberal ideologies that underpin the key competencies, and broader socio-cultural and social justice issues within their respective countries (e.g., Crick, 2008; Sjøberg, 2016; Takayama, 2013). This research investigated who and what influenced the design and implementation of the key competencies in the 2007 New Zealand Curriculum, and how students’ cultural diversity and identities were considered as part of this. Data for this case study were collected from three sources: interviews with key policy officials and academic consultants six years after the launch of the official curriculum; analysis of policy documents and discussion papers from government archives, and focus group interviews with teachers from two schools seven years into implementation. Bernstein’s (2000) theory of the pedagogical device, was used to focus analysis on the agents, influences, debates and events that impacted on the design and implementation of the curriculum. Fraser’s (1989) needs’ discourse theory was used to examine interpretations of cultural diversity and identity, and the implications of implicit valued attitudes and behaviours of the key competencies. Findings indicated that in the New Zealand educational policy context, the roles and interactions between agents and processes in the fields of production and reproduction were more ‘fluid’ and consultative than Bernstein’s (2000) structuralist model would suggest. This may be reflective of New Zealand’s small population and more informal collaboration between agents in different fields. The development of this curriculum prioritised the ‘process’ of understanding curriculum through consultation and feedback, compared to previous curricula which were more focussed on curriculum as a ‘product’. New Zealand’s socio-political climate, and its bicultural Treaty of Waitangi, appeared to impact on how the key competencies were conceived, and how student diversity and identity were interpreted at different points in the curriculum design and implementation process. Interviews with key policy officials and academic consultants revealed that cultural diversity was largely associated with ethnicity, and in particular, differences between indigenous Māori and Pākehā (New Zealand European). Less attention was given to the concept of multiple identities and intersections between ethnicity, socio economic class, gender and so on, and how these might influence interpretations of the key competencies. This was despite evidence of early discussion papers highlighting these complexities. At the curriculum implementation level, Bernstein (2000) argues that schools and teachers can often ‘reproduce’ middle class values and expected behaviours through ‘invisible’ pedagogical practices, with little awareness of potential disjuncts for disadvantaged groups. Yet he also states that this is not necessarily deterministic, and the finding for the two school focus groups demonstrated this. Despite no evidence that student diversity was a specific aspect of their professional development on key competencies, the teachers discussed some complexities of student diversity in their schools and how the key competencies might be interpreted in different ways. However, given the case study schools were considered to be particularly ‘diverse’, this type of discussion and consideration may not be typical of other New Zealand schools. The findings support the notion that the New Zealand curriculum key competencies were ‘weakly classified’ and ‘strongly framed’ (Bernstein, 2000). This means a high level of interpretation was located with school leaders and teachers, within the context of a permissive curriculum and thus presents both opportunities and risks. This case study highlights the importance of agents in every field understanding the complexities and implications of diversity in education. In addition, if the key competencies genuinely seek to enhance both vocational and social justice outcomes for a more cohesive and equitable society, then education for diversity would seem to be important. This research contributes new knowledge in relation to the process of curriculum design, highlighting the impact of a unique socio-political context on the interpretation of a curriculum construct, and the implications of ‘valued’ attitudes and behaviours of the key competencies on diverse students. It provides an example of how Bernstein’s (2000) theory of the pedagogical device can be used to identify important influences and processes that impact on the different stages of a curriculum design and implementation process. It also illustrates how the device can be usefully complemented by another theory, in this case Fraser’s (1989) needs discourse theory, to examine more closely the discourse that relates to a particular lens of the research.