Analysis of 65 children over a 4-year period on tests of operational and causal thinking offers support for Piaget's notion of stage progression. In kindergarten and grade one, the majority of children in this longitudinal study were between preoperational and the achievement stage of operational thought. By grade two, the majority had attained the terminal stage on seven of nine tests given. By grade three, the children achieved terminal stages on all tests. Over a 3-year period only eight true regressions occurred. This number constituted less than one percent of the total possible regressions. Both the Piaget test scores and the Wechsler Intelligence Scale for Children measures were slightly higher for the regressing children. In this study, "regressing children" were not less intelligent than nonregressing children. However, the numbers were too small to warrant any conclusions. (WY)