Content and Language Integrated Learning (CLIL) is an educational approach that uses a foreign, regional or an indigenous language to teach a school subject. This presentation describes a collaborative CLIL project which was conceived to investigate the effective ways of teaching different school subjects using English (foreign language) and Tahitian (indigenous language) in a French Polynesian elementary school context. The overall objectives of the project can be summarized as: identifying effective CLIL practices using English and Tahitian for beginner level elementary school learners through experimenting, collecting classroom data, analyzing, exchanging information, revising, and re-experimenting; and providing teacher development opportunities on the effective implementations of CLIL. This presentation explains how the data obtained from CLIL classrooms are employed to enhance teaching and teacher development practices. The first section of the presentation provides a synopsis of the CLIL approach and the principles on which it is based. The second section provides examples of classroom interactions from CLIL classrooms and how these data are utilized to enhance teaching and teacher development practices. The final part of the presentation describes the Socially Mediated Activity (SMA) framework, which we developed through our CLIL experiments for elementary school learners who had beginner level English and Tahitian.