The acquisition of ergative marking in Chintang (Sino-Tibetan, Nepal) seems challenging: the marker covers several functions but is rare in discourse because of NP ellipsis and syntactic constraints. Based on a longitudinal corpus of four children, we ﬁnd that children master the ergative only after age 4. Earlier usage tends to be limited to restricted lexical environments, and for one child also slightly biased to the agent function (which is the most frequent function). In addition we ﬁnd a linear increase in spontaneous usage, accompanied by a decrease of usages where the child models her usage on an immediately preceding usage by an adult. This suggests that ergative acquisition chieﬂy relies on imitating and extracting input patterns and less on exploring generalizations.