This article reports 2 experiments examining the changing role of iconicity in symbol learning and its implications regarding the mechanisms supporting symbol-to-referent mapping. Experiment 1 compared 18- and 26-month-olds' mapping of iconic gestures (e.g., hopping gesture for a rabbit) vs. arbitrary gestures (e.g., dropping motion for a rabbit). Experiment 2 replicated this comparison with 4-year-olds. All ages successfully mapped iconic gestures. Eighteen-month-olds and 4-year-olds but not 26-month-olds mapped arbitrary gestures, revealing a U-shaped developmental function. These findings imply that (a) there is no advantage for iconicity in early symbol learning and (b) the range of symbols mapped becomes more restricted at 26 months, re-emerging more flexibly during the preschool years. We argue that the decline in arbitrary gesture learning is a function of developing appreciation of communicative conventions. We propose that the re-emergence of arbitrary gestures at 4 years is driven by a wider range of symbolic experiences, and enhanced sensitivity to others' communicative intent. (Contains 1 figure and 2 tables.)