Young children's reasoning about ability was investigated among 155 preschoolers (M = 4 years, 10 months) across 3 studies. Results suggest that preschoolers are sensitive to mental state information when making judgments about another child's ability: They judged a child who finds a task easy to be smarter than one who finds the same task hard. Systematic patterns of errors on recall tasks suggest that preschoolers perceive positive correlations between (a) exerting effort and experiencing academic success, and (b) being nice and having high academic ability. Results from a comparison group of forty 9- to 10-year-olds (M = 9 years, 10 months) suggest that the preschool findings generally reflect emerging patterns of reasoning about ability that persist into later childhood, but that the perceived correlations between high effort and academic outcomes and between social and academic traits diminish with age.