This paper results from an ongoing investigation of the impact of a course of professional development [the Scottish Qualification for Headship (SQH)] on the practice of aspiring school leaders. It considers how conceptions of self as leaders and managers are affected by, and influence responses to, the management development programme offered. Our research indicates that where management identity and practices were 'immature' then SQH proved to be powerful in the permissions to manage which it offered in terms of both though and action, and in its impact on the development of professional identify. Where management identity and practice was more mature' then identity and practice were less open to influence and candidates tended to value SQH for its enhancement of specific management skills : despite these not being a prominent feature of the programme. The paper will explore the implications of the these findings for the nature of the provision of professional development for experienced professionals.