With Russian as the target language, a proof of concept study was undertaken to determine whether it is possible to identify linguistic features, control over which is implicated in progress on the Interagency Linguistic Roundtable (ILR) proficiency scale, thereby better to inform the instructional process. Following its development in an instrumentation study, a revised version of a computer-delivered battery of 33 perception and production tasks was administered to 68 participants--57 learners between levels 2 and 3 (21 at ILR 2, 18 at 2+, and 18 at 3) on the ILR scale, and 11 native speaker controls--whose proficiency was tested via an ILR oral proficiency telephone interview. The tasks sampled subjects' control of Russian phonology, morphology, syntax, lexis, and collocations. Relationships between control of the linguistic features and the ILR levels of interest were assessed statistically. All 33 tasks, 18 of which assessed learners' abilities in perception and 15 of which assessed their abilities in production, were found to differentiate ILR proficiency levels 2 and 3, and a subset was found to also distinguish levels 2 and 2+, and 2+ and 3. On the basis of the results, a checklist of linguistic features pegged to proficiency levels was produced that can be useful for syllabus designers, teachers, and learners themselves as well as providing the basis for future diagnostic tests.