Two experiments were designed to investigate the problems concerning awareness and solution of contradictions in length conservation tasks. In the first experiment, length conservation tasks, perceptual shade tasks and length measurement tasks were presented to 48 preschool and 46 first-grade children. The results showed that some non-conservers gave conservation judgement in perceptual shade conditions, and that a considerable number of non-conservers had already acquired length measurement schemata. It was suggested that difficulties of these non-conservers' awareness of contradictions were due to the weakness of existing primitive identity schema and no application of measurement schemata. In the second experiment, 63 non-conservers were divided into two groups. The results indicated that group I who were given verbal instructions in contradictory situations between perception and measurement showed a much more improved performance than group 2 who were not given them in such situations. It was suggested that without support of these instructions it was difficult for these children to solve contradictions, and that the solution of contradictions led to the construction of conservation schema.