Four liquid comparison tasks were designed to assess children's knowledge of functional relations, one-directional compositions of functional relations (greater + greater yield greater) and countervailing compositions (greater + lesser yield ?) in 4- to 7-year-olds. On one task, in which height indexed quantity, children of every age group performed well. Success on the other comparison tasks was related to operative level, as mdexed by conservation performance, and age. More advanced pre-operational children evidenced a degree of success on the one-directional composition task. Consistent with Schonfeld (1990), the results suggested that at more advanced operative levels: (1) the understanding of increasingly complex functional relations emerges and (2) thinking becomes increasingly exact. Correlational results revealed consistency across measures and factor-analytical findings suggested that a unitary developmental factor underlies performance differences. An attentional explanation of the findings was ruled out. The findings highhghted the multifaceted nature of children's progress toward integrating information from different dimensions of the comparison tasks.