When working together to enact new and challenging pedagogies, sharing classroom practice is a key resource to inform teachers' inquiry conversations. Understanding the role of trust in collaborative inquiry represents an important tension when teachers are sharing aspects of their work to interrogate and improve their practice. The study used a design-based methodology to explore the affordances of teachers' collaborative inquiry for teacher learning. Expanding the inquiry activity to include co-teaching created productive conditions to promote trust and support challenging conversations and thus had the potential to support teachers to transform mathematics teaching|learning.