Kotovsky and Gentner (1996) showed that presenting progressively aligned examples helped children discover relational similarities: Comparisons based on initially concrete and highly similar, but progressively more abstract exemplars helped the discovery of higher-order relational similarities. We investigated whether progressive alignment can aid learning of relational categories with either a deterministic (in which one relation reliably predicts category membership) or a probabilistic structure (in which each relation predicts category membership with 75% reliability). Progressive alignment helped participants learn relational categories with the deterministic structure. However, progressive alignment did not help participants learn the probabilistic relational categories. The results show that learning relational categories with a deterministic structure can be improved by progressive alignment, consistent with previous findings (Kotovsky & Gentner, 1996), but also support previous findings suggesting that relational categories are represented as a schemas, which are learned by a process of intersection discovery that fails catastrophically with probabilistic category structures.