The study compared the level of development observed in the imaginative play of young children with the level of development revealed in conservation an classification tasks. The sample included 40 children, with one 5/6-year old group of 20 children (10 boys, 10 girls), and two six/seven-year old groups of 20 children (14 boys, 6 girls). The children were observed in block and water play, in the housekeeping area; and 26 of them were administered five tasks of logical thinking. The tasks included measures of physical knowledge: conservation of mass and classification of beads, and measures of social knowledge: conservation of social role, classification of boys and girls, and kinship. The results supported the question of a parallel correspondence between stages of development exhibited in paly and in logical thinking. Some age differences appeared in the observational measure of social interaction in children's play. All younger children adopted individualized rules and felt rules were fixed. Some, but not all older children maintained a cooperative system of interaction, developing rules by consensus. Implications for the early childhood caregiver were described, based on the informal, interactive social context which supported the development of rules. (Author)