Background: Teachers’ support for addressing cisgenderism and cisnormative cultures in schools is necessary to support students’ freedom to express gender in expansive ways and to embrace trans identities. However, few questions are asked about how primary school teachers grapple with trans identities in South Africa. Purpose: The article fills this gap by focusing on how school teachers negotiate their understandings of gender identity and gender expression by showing their capacities and potential in creating a trans-affirmative climate in primary school. Participants: Participants were 30 self-identified heterosexual primary school teachers of diverse race and class backgrounds who were located in one primary school in South Africa. Research Design: This qualitative study employed in-depth face-to-face and telephone-based semi-structured individual interviews. The article draws from new feminist materialist approaches to “assemblages” and decolonial thinking to consider how participants negotiated gender expectations. Findings: Trans identity is conflated with being gay and misrecognized through a reliance on historically produced religious and cultural norms that are part of the colonial and apartheid legacies in South Africa. While the trans assemblage shows potential to challenge and question the sex-gender conflation, historical legacies, suffused with cis-heteronormative logics, lead to a fundamental misrecognition and erasure of trans as a sign of being gay. Conclusions/Recommendations: The utility of a decolonial trans assemblage is evident in examining how epistemic erasure occurs through historical mechanisms, while denaturalizing the reliance on binary gendered systems and Western knowledge. If primary schools are to support gender-expansive ways of being, addressing how historical processes, cisgenderism, and cisnormative cultures permeate teachers’ understanding of gender remains vital work.