This book is above all a practical guide for young teachers of French as a foreign language. It is composed of two parts: a part that analyzes the theoretical aspect of the concept of differentiation, then a practical implementation in French as a foreign language classes, with the CAVILAM - Alliance française, in Vichy, as a setting. Readers will also find a grid summarizing concrete answers provided by didactic theory and classroom experiences in order to take advantage of the heterogeneity of the class.