This article draws on research conducted over two years in the North West of England and is located in the context of workforce remodelling. It examines how the higher level teaching assistant (HLTA) role has developed and is appraised and suggests that the anomalous nature of the role, which often relies on the enactment of observed teacher performance, and the ambiguous, localised, niche roles which have developed, render measurement of impact problematic. The performance of HLTAs is assessed using a vocational model which relies on retrospective self-assessment of competence and the article draws on Foucault's (1988) concept of "technologies of the self" to examine the implications of using this approach. The article also suggests that the use of predominantly self-assessment to measure competence is problematic and applies Kruger & Dunning's (1999: 1122) notion of the "unskilled and unaware" to argue that lack of contextualised and specialised knowledge can lead to "inflated self-appraisals".