An 18-month study of the development of communicative competence in three Kaluli children from Papua, New Guinea, shows that Kaluli children use pragmatically appropriate word order before they correctly indicate "agent" by casemarking. In Kaluli, pragmatic concerns determine word order. The noun which the speaker intends to focus on is placed immediately before the sentence-final verb. There are two casemarking systems. The ergative system, used in Object-Subject-Verb (OSV) sentences, requires that the subject of a transitive verb receive the ergative case marker, and the object of transitive and the subject of intransitive verbs receive the absolutive case marker. The neutral/ergative system, used in SOV sentences, calls for a neutral case marking for Agent and Object. Findings of the study show that in OSV sentences, correct word order for expressing focus preceded casemarking in the children's speech. Once the marking was acquired, children could contrast agent focus within and across turns at talk by word order and casemarking. Marking in SOV sentences was acquired in three stages: (1) no agent marking, (2) incorrect ergative marking of sentence-initial agents, and (3) correct restriction of ergative marking to OSV sentences. By 32 months, all three children were controlling word order and casemarking, the former preceding the latter. (PJM)