This thesis examines the processes and outcomes of a composer-teacher's practice in the context of a New Zealand secondary school. The research was undertaken by the composer-teacher/researcher as a case study that integrates an investigation of the context with four action research music composition projects developed as a creative response to that context. Chapters One to Three comprise the background theory. Chapter One provides an introduction and overview of the research; Chapter Two explains and justifies the research methods. Chapter Three peels away and examines five layers of the secondary school context identified as significant in shaping the perceptions of the participants: approaching the context in a multi-layered way enabled coherent synthesis and appraisal of the relevant literature. Chapters Four to Seven comprise the four action research music composition projects. Each action research project focuses on a music score composed by the composer-teacher/researcher for a specific group of students at Macleans College, Auckland. The composition, production, and performance processes are investigated from the perspectives of all the participants. Each music project comprises a four part progression - plan (composition process), data (music score), data analysis (recordings of performances, surveys, and interviews with all participants) and reflection (feedback, and feedforward into the next project). Each phase of the research generated significant outcomes, such as the four original music scores. Chapter Eight summarizes the themes, issues, and patterns that emerged, and makes recommendations for further research. A model of co-constructive practice emerges from this research: teacher and students co-construct artistic worlds through performance. The model is not new (it is common practice, adopted by generations of musician-teachers) but is rarely acknowledged and currently un-researched. This research demonstrates the validity of the practice from both musical, and teaching and learning perspectives, and examines the strengths and limitations of the model. At its best, the creative processes co-constructed by a teacher with her students are shown to provide a crucible within which intense and creative learning experiences occur. Students of all levels of ability are shown to gain confidence in this context, and subsequently develop skills with apparent ease. The co-constructive model is limited in that it cannot meet the musical needs of all students: co-construction should be considered as one model of practice, appropriate for use in association with many others. This research provides 'virtual access' to a particular world of performance practice, revealing the secondary school context as a realm of authentic and valid musical practice.