The purpose of this research was to test the predictions of the Accessibility Hierarchy (AH) theory (Keenan & Comrie, 1977) applying it to the Russian language. According to this theory, relative clauses are acquired in a fixed unidirectional order. Since some researchers (Hamilton, 1994) claim that the AH is multidirectional, this study takes into consideration these findings as well. In this study, three types of error, incorrect adjacency, incorrect morphological relative clause ending, and pronoun retention, were analyzed separately. In addition, the acquisition of pied-piping structure in the marked relative clauses was investigated. The results of the research support Hamilton’s findings and suggest that generalization is clearly not unidirectional. Regardless of type of instruction the participants of both groups generalized their learning in both directions. However, in pied-piping structure the complex treatment group outperformed the basic treatment group.