In this paper we discuss the acquisition of the voicing system of Malagasy, an Austronesian language. Our study is based on the longitudinal data of three children ages 19-32 months, and is to our knowledge the first systematic investigation of the acquisition of Malagasy. The Malagasy voicing system has a distinctive morphology and involves the promotion of an argument (actor, theme, instrument, etc.) to a referentially and syntactically prominent position, typically clause-final. We look at two competing accounts of the Malagasy voicing system, one in which the promoted argument is analyzed as a subject and the promotion operation an instance of A-movement (Guilfoyle, Hung, & Travis, 1992) and a more recent account in which Malagasy is analyzed as a V2-like language in which the promoted argument is a topic and the promotion an instance of A'-movement (Pearson, M. (2001); Pearson, M. 2005)). Both analyses have clear implications for acquisition, which we examine in this paper. Our acquisition results favor the analysis of the promoted argument as an A'-element. We also show that there is a developmental stage in Malagasy that parallels the root infinitive (RI) stage widely observed in various European languages. Apparent differences between the Germanic RIs and the analogous phenomenon in Malagasy are derived from differences in the functional structure associated with a voicing system as opposed to an agreement system.