AS PART OF THE EVALUATION OF EFFECTIVENESS OF FULL-YEAR HEAD START PROGRAMS, CHILDREN FROM A NATIONWIDE SAMPLE OF CENTERS WERE TESTED WITH FIVE INSTRUMENTS (PEABODY PICTURE VOCABULARY TEST, PRE-SCHOOL INVENTORY, VINELAND SOCIAL MATURITY SCALE, DRAW-A-PERSON, AND BEHAVIOR INVENTORY). CENTERS WERE SELECTED TO BE REPRESENTATIVE OF PROGRAMS OF DIFFERENT LENGTHS. POST-TESTS WERE USED TO EXAMINE THE QUESTION OF WHETHER THE LENGTH OF THE PROGRAM AFFECTS THE PERFORMANCE OF THE CHILDREN. THERE WAS NO RELIABLE EVIDENCE OF A SYSTEMATIC RELATIONSHIP BETWEEN LENGTH OF PARTICIPATION IN A PROGRAM AND LEVEL OF PERFORMANCE OR DEVELOPMENT. FACTORS AFFECTING THE INTERPRETATION OF RESULTS ARE DISCUSSED IN THIS REPORT. (DESCRIPTIVE STATISTICS ON THE TEST SCORES, CHARACTERISTICS OF PARENTS, FAMILIES, AND STAFF MEMBERS ARE PRESENTED. INTER-TEST CORRELATIONAL DATA ARE REPORTED.) A SUMMARY OF THIS REPORT IS ALSO AVAILABLE AS A SEPARATE DOCUMENT. (LG)