This paper presents a study designed to clarify the role of perceptual-attentional factors in the development of conservation, and relates the results to procedures for assessing conservation. Subjects were 192 first and second graders. The number and type of perceptual cues in the conservation of liquid quantity task were systematically varied. In general, nonconservation increased in kindergarteners as the number of cues increased. In contrast, first graders were affected very little by the perceptual conditions. Both grades showed a specific training effect of borderline significance under certain conditions. The results suggest that the development of conservation involves several levels which vary from an early understanding of invariance which can be demonstrated only under facilitating conditions, to a final, stable, generalized concept of quantity. (Author/CS)