Spatial representation and reasoning are important in cognition, yet they are challenging for children. Research has shown that comparison can support learning about common spatial structure and that using common labels can facilitate this process. Here, we show that a comparable pattern holds for learning about differences. That is, contrastive labels can promote comparison-based learning of key spatial differences. In two experiments, 5- to 7-year-old children were asked to learn a key engineering principle--namely, that diagonal braces confer stability in building structures. Two factors were varied between subjects: the alignability of the training exemplars, and whether a contrastive label was used. Learning was assessed through a variety of transfer tasks, both immediately and after a delay of 2-5 days. The results showed that children in the high-alignment condition performed better than those in the low-alignment condition, replicating previous findings. Further, children who received the contrasting brace label performed better than those who did not. This suggests that hearing contrastive language can invite structural alignment and reveal differences that inform children's learning. We discuss broader implications for cognition and education.