Creating correct shape categories requires young children to overcome reliance on perceptual features and surface similarity as cues for membership and to use abstract rules as bases for categorization (e.g., triangles are enclosed shapes with three sides). Relying on surface similarity, children often wrongly include non-triangles that resemble familiar triangles in the triangle category, and exclude unfamiliar actual triangles. This study attempted to improve preschool-age children’s triangle categorizations by presenting structurally aligned comparisons that either shared a common structure or that highlighted a contrasting structure. Across both types of comparisons, the exemplars were either highly or lowly superficially similar (both variables manipulated between subjects). We hypothesized that low-similarity common-structure comparisons would support extension of the triangle category beyond prototypical exemplars, while high-similarity contrastive alignments would highlight category boundaries. Preliminary results suggested that improvement in categorization accuracy was primarily driven by a reduction in erroneous identification of a non-triangle as a triangle.