In this manuscript we provide an overview of several studies on the processes cognitive involved in rea-ding and writing in immigrant students whose native language does not matches the language of instruc-tion. The first major study aimed to analyze the cognitive processes and reading of Spanish-speaking children learning English as a second language. In the second study, the aim was to analyze the cognitive processes of writing. Measures were taken of linguistic competence (vocabulary and syntactic awareness), working memory, phonological awareness and reading and writing of words and pseudowords in English for the monolingual group and the same measures in English and Spanish for the Hispanic group speakers. Both studies were carried out in Canadian schools of the district of Vancouver in the Canadian province of British Columbia (British Columbia). The main findings of these studies support the hypothesis of lin-guistic interdependence, as has been demonstrated that the skills of both reading and writing are closely related between both languages.