A STUDY WAS CONDUCTED TO FIND OUT WHAT MENTAL PROCESSES ARE INVOLVED IN THE DEVELOPMENT OF THE CONCEPT OF CONSERVATION OF CONTINUOUS QUANTITY, AT WHAT AGES THESE PROCESSES ARE DEVELOPED IN CHILDREN, AND WHETHER THEY ARE ADEQUATELY EXPLAINED BY PIAGET'S THEORY. ONE HUNDRED 5.75 TO 7-YEAR-OLDS WITH A MEAN I.Q. OF 105 WERE PRETESTED AND CLASSIFIED AS CONSERVERS, NON-CONSERVERS, OR PARTIAL CONSERVERS. HALF OF THE NON-CONSERVERS AND HALF OF THE PARTIAL CONSERVERS WERE GIVEN 1 15-MINUTE TRAINING SESSION (USING CONTAINERS OF LIQUID) BASED ON THE THEORY THAT THE MENTAL PROCESSES NEEDED FOR CONSERVATION WERE (1) RECOGNITION OF IDENTITY (QUALITY OF QUANTITY REMAINS UNCHANGED EVEN IF TRANSFORMED, (2) A LOGICAL MULTIPLICATIVE OPERATION (ALTERATION IN HEIGHT OR WIDTH MIGHT BE COMPENSATED FOR BY THE OTHER), AND (3) OPERATIONAL REVERSIBILITY (QUANTITIES ARE UNCHANGED IN RECIPROCAL OPERATION). A MATCHED CONTROL GROUP HAD NO TRAINING. POSTTEST I (THE PRETEST) RESULTS SHOWED THAT ALL BUT 4 OF THE CHILDREN TRAINED WERE RECLASSIFIED AS CONSERVERS. A DIFFERENT POSTTEST GIVEN TO ALL 100 SUBJECTS SHOWED THAT CONSERVER LEARNING WAS RETAINED AND TRANSFERRED, SUGGESTING THAT 1 OR ALL OF THE SUGGESTED MENTAL PROCESSES MUST BE NEEDED AS PIAGET'S THEORY CLAIMS. HOWEVER, THEY MAY EXIST IN CHILDREN AT AGES EARLIER THAN PIAGET PREDICTED. (MS)