In line with cross-linguistic research aiming at identifying criterial features that discriminate the CEFR proficiency levels, the study investigates language elements that are core characteristics of each proficiency level for Greek L2. It is based on a graded corpus of 150 written narratives produced by young L2 learners (aged 8-14) at levels A2 to B2. This corpus was annotated with respect to linguistic features such as clause subordination, discourse markers, modifiers and grammatical accuracy. On the basis of statistical analysis, a number of indices are put forward as criterial features discriminating language proficiency levels in L2 Greek narratives: text length, frequency of dependent and centre-embedded clauses, felicitous uses of clitics, use of evaluative adverbs and adjectives, and additive discourse markers.