THIS STUDY EXAMINES THE PROGRESS OF 125 CHILDREN IN THE CLEVELAND PUBLIC SCHOOL KINDERGARTENS WHO ATTENDED HEADSTART DURING THE SUMMER AND 125 CHILDREN IN THE SAME SCHOOLS WHO DID NOT ATTEND THE HEADSTART PROGRAM. SOME INDICATIONS IN THIS STUDY SUGGEST THAT A HEADSTART CHILD SHOWS MUCH GREATER VARIABILITY IN HIS CONCEPTUAL DEVELOPMENT THAN A NON-HEADSTART CHILD. HE ALSO TENDS TO PERFORM BETTER IN THE AREAS OF COLOR AND FORM DISCRIMINATION AND POSSIBLY GROUPING WHEN HE IS IN A NON-HEADSTART TEACHER'S CLASS. IN A HEADSTART TEACHER'S CLASS, THE HEADSTART CHILD SEEMS TO ACHIEVE IN THE MORE ORGANIZATIONAL AREAS, AS BEST REFLECTED IN INCREASED VERBAL FACILITY IN THE TIME SEQUENCE AND ORDERING CONCEPTS. THE RESULTS OF THIS STUDY RAISE THE QUESTION OF WHETHER THE IMPACT OF A STIMULATION EXPERIENCE CAN BE MAINTAINED. FOLLOWUP STUDIES AND EVALUATION OF DEMONSTRATION PROJECTS REPORT THE PHENOMENON OF THE DECREASING DIFFERENCE OF SUCCESS BETWEEN THE EXPERIMENTAL AND CONTROL GROUPS. (CO)