Mentoring is a practice widely utilised to support new teachers. However, in locally formed systems, the practice of mentoring is conditioned by traditions and arrangements specific to the site. To understand ‘good’ mentoring, these local arrangements cannot be ignored. In this article, the theory of practice architectures is employed to make explicit the prefiguring arrangements of mentoring practices in Finland and NSW Australia. The findings suggest that mentoring practices are shaped by their ontological specificity and this makes reproducing mentoring practices in different sites problematic. Explicating the prefiguring architectures of practices is critical to understanding the contested nature of mentoring.