a comparative study of bilingual and monolingual iranian efl students’ knowledge of english grammar and vocabulary: a cognitive approach

presenting a brief description of bilingualism and its correlation with cognitive development and 3rd language learning, the present research primarily aims to compare the knowledge of english vocabulary and grammar in a sample of monolingual and bilingual high school students (fourth graders) of fars and khuzestan provinces in iran. to fulfill this objective, 448 monolingual and bilingual students were selected from among 67031 students in the 2012-2013 academic year. they were given a proficiency test, and the results were analyzed through spss computer program. the findings revealed that contrary to a considerable number of researches, bilingualism here is not significantly correlated with the students' knowledge of english vocabulary and grammar. in other words, monolingual participants outperformed their bilingual counterparts in the test. based on the results of the study, it is suggested that further researchshould be conducted in these bilingual communities to explore the hidden factors associated with lower or weaker performance of bilinguals in learning english language.