Words influence cognition well before infants know their meanings. For example, three-month-olds are more likely to form visually based categories when exemplars are paired with spoken words than with sine-wave tones, a likely precursor to learning symbolic relations between words and their referents. However, it is unclear why words have these effects. In 3 experiments we tested the hypothesis that exaggerated “showing” gestures used when naming objects, and the resultant cross-modal synchrony between a name and object motion, can affect object categorization. Participants were 119 3-month-old infants (56 were female and 63 were male). According to caregiver report, the sample was composed of European American (N = 114) Black (N = 6), Hispanic (N = 2) and multiracial (N = 6) infants. Participants were growing up predominantly in homes with at least 1 parent who completed a college education or a higher degree (80%), and the remaining 20% completed high school. After replicating evidence that words and tones have different effects on categorization, we found that prefamiliarizing infants with tone-object synchrony leads tones to influence categorization as words do. Moreover, we found that concentrated experience with word-object synchrony enhances the effects that words themselves have on categorization.