This study investigated second‐language (L2) learning to gain a better understanding of learning mechanisms that also operate in child first‐language (L1) learners. The research was inspired by research on the beneficial effects of child‐directed speech (CDS). We tried to examine whether such benefits can be observed in the domain of inflectional morphology in adult L2 learners. Specifically, we investigated whether one typical feature of CDS, diminutivization, can facilitate learning of Russian gender. Diminutives (i.e., the translational equivalent of doggy, birdie, etc.) are a pervasive feature of Russian CDS. Olmsted (1994) suggested that the frequent use of diminutives in Russian CDS may facilitate the child's acquisition of grammatical gender because it eliminates nontransparent morphophonological marking. To examine the effect of diminutives on gender learning directly, adult native speakers of English were taught a variety of Russian nouns, with half of the participants trained on diminutive nouns and half on the nondiminutive base forms. Over 4 sessions, participants learned to use color adjectives to name the color of the objects depicting the nouns. In Russian, adjectives have to agree in gender with the nouns they modify; correct adjective agreement was used as a measure of gender learning. The diminutive training group demonstrated better learning of noun gender and better generalization to novel word forms and novel nouns, thus confirming the beneficial effects of diminutives on gender learning. The observed diminutive benefit for gender agreement has subsequently been demonstrated in Russian children (Kempe, Brooks, Mironova, & Fedorova, 2003), both for familiar and, in even more pronounced ways, for novel nouns, thus confirming the generalizability of the results to L1 learners. In light of these later findings, the present study underscores the importance of complementary research in L1 and L2 learning so that important questions about the nature of L1 acquisition may be answered by means of controlled manipulation of the language input in L2 learning.