Early bilingualism is thought to facilitate language learning [Klein, E. C. (1995). "Second versus third language acquisition: Is there a difference?" "Language Learning", 45(3), 419-466; Cromdal, J. (1999). "Childhood bilingualism and metalinguistic skills: Analysis and control in young Swedish-English bilinguals." "Applied Psycholinguistics", 20(1), 1-20]. The present study tests whether experience with formal study of an L2 conveys further advantages to early bilinguals, and whether typological similarity of previously-learnt languages to L3 plays a significant role in L3 learning. Two groups of participants, Early Bilinguals (EBLs) and Early Bilinguals with formal L2 experience (EBLs+L2), were tested on acquisition of Korean case markers in four argument structures: intransitive verbs, transitive verbs with both arguments, transitive verbs with one omitted argument, and descriptive verbs. EBLs+L2 significantly outperformed EBLs and the two groups showed further differences by sentence type, with EBLs showing more difficulty with novel structures while EBLs+L2 did not. To examine the role of typological proximity, EBLs+L2 were divided into those who had studied Japanese (EBLs+Jap), which is structurally similar to Korean, and those with experience studying other languages (EBLs+non-Jap). In spite of typological similarity, EBLs+Jap did not significantly outperform EBLs+non-Jap overall. These results support the conclusion that formal study of an L2 conveys advantages to early bilinguals in L3 learning. Such experience results in greater metalinguistic awareness, allowing students to efficiently acquire structures that differ from their existing linguistic repertoire.