A study of the acquisition of ergative case-marking (ECM) in Samoan indicates that it rarely appears in the speech of 2–4 year old children. It is argued that the late acquisition of ECM is caused primarily by the fact that expression of the case-marker in adult Samoan is sociolinguistically variable, with speech between household members showing the lowest frequency of expression of the case-marker. However, evidence suggests that Samoan children encode ergative distinctions through word order, in that they tend to reserve the position immediately following the verb for absolutive constituents.