This paper presents a study aiming at the identification of language features that can be employed as criteria for assessing language proficiency of elementary school students who learn Greek as a second language. A graded corpus of written narratives was compiled and annotated with respect to linguistic features that, according to previous research, are indicators of language development, i.e. clause subordination, discourse markers, modifiers and grammatical accuracy. Analysis of data revealed that certain features, such as the use of evaluative adverbs, have discriminatory properties and can thus contribute to the allocation of a learner’s written production to a proficiency level as defined by the “Common European Framework of Reference for Languages”.