This article revisits a previous publication which questioned how Teaching Assistants (TAs) manage behaviour in mainstream English primary schools (Clarke and Visser, 2016). That paper highlighted the lack of specific research in the area and noted, that despite increases in research on TAs work, there remained a lack of understanding in relation to how TAs supported children's non-academic or 'soft skills'. Following on from that, this article details the findings of a doctoral research project that investigated factors that constrained and supported TAs' management of behaviour. Using the findings from that research, this article offers answers to the to the question I outlined in the previous publication 'Teaching Assistants managing behaviour -- who knows how they do it?' (Clarke and Visser, 2016). Concepts including TAs' understanding of their 'place', the impact of agency and how consistency in a range of areas influenced the agency TAs experienced in managing behaviour will be discussed.