This document provides an overview of Cultural-Historical Activity Theory (CHAT) and its application to analyzing teacher training. It discusses CHAT's key concepts, including activity systems, contradictions, expansive cycles, and mediation by tools. The researcher plans to use CHAT to study how 7 student teachers in Spain develop skills through collaboration with peers during their practicum. Data sources will include discussions, presentations, and assignments. Action-relevant episodes will be identified and contradictions analyzed to understand how theoretical and practical knowledge are connected through social interaction.