This book is an attempt to study the incidence of bilingualism on the language achievement of Tashelhit speaking pupils in Morocco, viz. , it tries to assess the role played by linguistic, psychological, socio-economic and cultural factors in the pupils' level of performance in school. Specifically, it provides an analysis of the impact of a given language on the mental activities of the learner, the contamination of French by Arabic or Tashelhit and vice-versa, and the pupils' attitudes towards code-mixing. These language behaviours are considered in relation to language performance. Additionally, it explores the possible correlations that exist between the learner's achievement in school and his parents' involvement in his studies, the level of education of his father and his occupation.