In the context of English language teaching in non-linguistic Russian universities differentiation is necessary to ensure every student language development in typically mixed ability groups of students. The paper discussed the reasons for implementing differentiated English language instruction into the practice of tertiary language education and states the lack of research into this area. Research is needed to provide research-based evidence to support activity modification as an efficient tool of differentiated language instruction in Russian non-linguistic universities. Differentiated instruction principles are being discussed and activity/task modification matrix is being proposed to guide English language university teachers in the absence of differentiated instruction focus both at the stage of pre-service teacher education and at the stage of further in-service teacher training and development.