Three studies examined development of the perception of temporally unidirectional transformation, such as dropping blocks, with 3.5- to 6.5-year-olds who compared forward and backward videotapes of events or made individual judgments of what would happen if action were attempted. Findings indicated that even 3.5- to 4.5-year-olds recognized the anomaly of backward versions of gravity and separation events. Relatively few predicted impossible transformations in the prediction task. (Author/KB)