This article examines the impact of academisation on English Sixth Form Colleges through the lens of the Principals and Governors who lead such organisations -- those who have decided to opt for academisation, and those who have not. A comprehensive survey of the Principals or Chairs of 35 Sixth Form Colleges, representing all regions of England, supplemented by a small number of follow-up interviews, generated five distinct but overlapping themes that seemed to resonate with the majority of respondents: Autonomy, Funding, Local Circumstances, Strategy and Quality. Unpacking these themes and identifying their inter-relationships could be helpful to those leading Sixth Form Colleges considering academisation, as well as providing a research framework for future work and a distinctive contribution to the theoretical literature. We believe we demonstrate that academisation can be seen as a significant example of how the marketisation of education has created an illusory set of market freedoms commonly held to be achievable through academisation, that are in fact highly constrained by government policy and accountability mechanisms. The article concludes by considering some implications of the data and our analysis for policy and practice in the Sixth Form College sector, and some suggestions of where further research is urgently needed.