The purpose of this paper is to discuss the impact of the Curriculum Design Coherence Model (CDC Model -- Rata, 2019) on the design practice of two music teachers in a middle school music class in New Zealand. The CDC Model proposes that deep learning first requires deep design coherence. This coherence is generated by three interrelated design dimensions: (i) the 'surfacing' of epistemic structure, (ii) the use of subject concepts and (iii) the interrelationship between 'knowledge-that' (knowledge of something) and 'know-how-to' (knowing how to do something with that knowledge of something). We discuss how the model has been put to use in the design of a song writing unit of work for students aged 10-12 years in a general music class and note the impact of the model on the developing design expertise of the two music teachers involved in a wider research project.