Background: In the past decade, educational settings worldwide have experienced a significant increase in the number of school-based teaching assistants (TAs). The deployment of these TAs has been accompanied by reports of confusion and uncertainty about their roles and responsibilities within schools. While the need to reframe the role and purpose of TAs is recognised, it remains unclear how this can be best achieved. Purpose: The purpose of the study is to explore the ways in which one group of TAs deployed in Hong Kong schools construct their professional identities, to understand the constraints and enablements to these processes, and to consider how different stakeholders might be able to best support this identity work. Sample: The primary participants in this study are nine English language teacher assistants employed at different schools across Hong Kong. Other participants include full-time English language teachers who have experience of working with one of these TAs, as well as students who attend English language classes in which these TAs participate. Design and methods: A qualitative multiple case study approach is adopted. In-depth interviews with TAs, teachers and students are used to gain a contextualised interpretation of the primary participants' experiences of constructing professional identities within schools. A multilevel, multidimensional theoretical framework, which considers identity construction as both a discursive and experiential accomplishment, is then used to understand the constraints and enablements TAs experience in constructing these identities. Findings: Results indicate that TAs face challenges in constructing their professional identities at institutional, interpersonal and intrapersonal levels within Hong Kong schools. In addition, the TAs believe that exercising agency to contest their positionings within schools is often insufficient to place them on a trajectory towards become a teacher. The results also suggest that the identity