THE PURPOSE OF THIS STUDY WAS TO FIND OUT WHETHER SOCIAL CLASS DIFFERENCES IN INTELLECTUAL DEVELOPMENT ARE PRESENT IF (1) CHILDREN FROM SOCIALLY DISORGANIZED SLUM FAMILIES ARE COMPARED WITH CHILDREN FROM STABLE, LOW INCOME AND MIDDLE INCOME FAMILIES, (2) THE PIAGET OBJECT SCALE, A NEW MEASURE OF COGNITIVE DEVELOPMENT BASED ON PIAGET'S SENSORIMOTOR OBSERVATIONS, IS EMPLOYED, AND (3) EFFORT IS MADE TO OVERCOME ANY MOTIVATIONAL FACTORS ABLE TO INTERFERE WITH TEST PERFORMANCE. IN A CROSS-SECTIONAL APPROACH, 184 NEGRO CHILDREN, OF 12, 18, AND 24 MONTHS OF AGE REPRESENTING 3 SOCIOECONOMIC STATUS GROUPS, WERE COMPARED ON THE PIAGET OBJECT SCALE AND THE CATTELL INFANT INTELLIGENCE SCALE. RESULTS SHOWED NO DIFFERENCES AMONG THE 3 GROUPS ON EITHER SCALE. HOWEVER, INFANTS WERE RATED ON SUCCESS OR FAILURE ON A GIVEN ITEM WITHOUT REGARD TO THE NUMBER OF TRIALS OR TIME REQUIRED, SO SOCIAL CLASS DIFFERENCES MAY HAVE BEEN HIDDEN. PREVIOUS RESEARCH FINDINGS WHICH INDICATED THAT SOCIAL CLASS DIFFERENCES IN INTELLECTUAL DEVELOPMENT DO NOT APPEAR DURING THE FIRST 2 YEARS WERE CONFIRMED. AFTER 2 YEARS LANGUAGE BECOMES IMPORTANT FOR LEARNING, AND DIFFERENCES ARE NOTED. DIFFERENCES IN PATTERNS OF MOTIVATION AND COGNITIVE STYLE OCCUR EARLY BUT SHOW UP IN LATER LEARNING. THEREFORE, COMPENSATORY EDUCATION PROGRAMS SHOULD FOSTER THE KINDS OF MOTIVATIONS AND COGNITIVE SKILLS WHICH WILL BE NEEDED FOR ABSTRACT THINKING AND ACADEMIC SUCCESS. THIS PAPER WAS PRESENTED AT THE MEETING OF THE SOCIETY FOR RESEARCH IN CHILD DEVELOPMENT, (NEW YORK CITY, MARCH 30, 1967). (MS)