The objective of this study was an attempt to clarify the nature of number conservation with number conservation tasks using variations in length, area, and volume. According to Piagetian theory, conservation is attained successively for number, length, area, and, finally, volume. It was hypothesized that success on the number conservation tasks involving length, area, and volume would follow the same order suggested by Piaget's research. To test the hypothesis, a constructed probability distribution derived from Piagetian theory and a scalogram analysis were used. Eighty children from four to seven years old composed the sample. The hypothesis was not confirmed. In particular, relative to the constructed probability distribution analysis, the order of development of number conservation involving length, area, and volume is individual in nature, while the scalogram analysis suggested no one general order of difficulty of the tasks. (Author/JM)