Does spatial language contribute to the growth of preschool children's spatial skills? Four-year-old children (N = 50) were randomly assigned to a play-only (n = 24) or a spatial-language and play condition (n = 26). Their mental rotation and spatial vocabulary were assessed at baseline and several days after 5 play sessions. Children in the spatial-language condition scored higher at posttest on a mental rotation task than those in the play-only condition. The amount and diversity of experimenter spatial language during the play sessions accounted for a significant amount of the variance on children's posttest mental rotation. Significant gains in mental rotation were replicated in a second study (N = 34) with a broader range of play activities and with children enrolled in Head Start. These results show that the facilitative effects of spatial language on spatial cognition are not restricted to the context in which the spatial language is provided. In particular, 4-year-old children's experience with spatial language during play can transfer to promote their mental rotation. (PsycInfo Database Record (c) 2020 APA, all rights reserved).