Spatial skills are consistently linked to mathematical reasoning, and are sensitive to intervention. One important spatial skill is spatial scaling. We evaluated whether (1) a playful scaling game might promote learning by providing feedback during play, and (2) spatial scaling is related to number-line estimation based on the mutual reliance on relative magnitude reasoning. Forty-eight children, ages 5.5-8.3, completed a playful scaling game and a number line estimation task. Results show that children improve from the first to second half of the task, especially for more difficult trials and for the lowest-performing children. In addition, scaling and number-line estimation relate when controlling for age and vocabulary. Similar improvement on the task and relations to number-line estimation were observed in a conceptual replication (N=52). These results provide support for further study of improving spatial scaling in children, with the possibility to test whether scaling could support related mathematical skills as well. [This paper was published in "Mind, Brain, and Education" v12 2018.]