Μαρία Πλαδή, Αρετή Οκαλίδου & Βιργινία Παπαγεωργίου - Πανεπιστήμιο Μακεδονίας This paper, part of an on-going project on bidialectal communities, seeks to describe and quantify the prevalence of the local dialect in the school environment, where only Standard Modern Greek is taught. It also aims at investigating the factors that are related to the use of dialect elements in pupils’ linguistic performance in the bidialectic environment of Pyrgi in Chios and Litohoro in Northern Greece. Linguistic data from these two different geographic areas were collected and both the oral and written production of students was analyzed. Dialectal interference was measured in terms of phonology, morphology and lexicon. ΛΕΞΕΙΣ-ΚΛΕΙΔΙΑ: διαλεκτική παρείσφρηση/παρεμβολή, διάλεκτος στην εκπαίδευση, διδιαλεκτική εκπαίδευση, προφορικός και γραπτός λόγος