TO DETERMINE WHETHER SIGNIFICANT DIFFERENCES EXIST IN SKILL PERFORMANCE AS A RESULT OF HEAD START EXPERIENCE AND TO DETERMINE WHETHER THESE DIFFERENCES EXIST BETWEEN TWO ETHNIC GROUPS, 17 ANGLO-AMERICAN AND 62 MEXICAN-AMERICAN CULTURALLY DISADVANTAGED CHILDREN WERE PRE-TESTED AND POST-TESTED DURING THE SUMMER OF 1965 IN CONNECTION WITH SIX-WEEK HEAD START PROGRAMS IN COSTA MESA AND FULLERTON, CALIFORNIA. FIVE TEACHERS USING MODIFIED MONTESSORI MATERIALS STRESSED THREE DEVELOPMENTAL AREAS, (1) PERCEPTUAL-MOTOR, (2) SOCIAL-EMOTIONAL, AND (3) INTELLECTUAL-ACADEMIC. SEVEN INSTRUMENTS WERE USED TO TEST THE PROGRAM'S EFFECTIVENESS--GESELL MATURATION INDEX, MATEER INVERSION TEST, TESTS OF DOMINANCE, TEACHER RATING SCALE, GOODENOUGH-HARRIS D-A-P, PEABODY PICTURE VOCABULARY TEST, AND WIDE RANGE ACHIEVEMENT TEST. RESULTS SHOWED THAT CERTAIN HANDICAPS DO EXIST AMONG CULTURALLY DISADVANTAGED CHILDREN PRIOR TO SCHOOL EXPERIENCE AND THAT POSITIVE GAINS OCCURRED WHEN ENRICHMENT EXPERIENCES WERE PROVIDED. GREATEST GAINS WERE IN THE AREAS OF INTELLECTUAL-ACADEMIC AND SOCIAL-EMOTIONAL SKILLS. ETHNIC DIFFERENCES APPEARED IN THE LINGUISTIC SKILLS LIMITATIONS OF THE MEXICAN-AMERICAN CHILDREN. NEED FOR MEDICAL AND DENTAL ATTENTION WAS APPARENT IN BOTH GROUPS. FUTURE PROVISION SHOULD BE MADE FOR CONTINUED PRESCHOOL EDUCATION AND WIDER DISSEMINATION OF HEALTH SERVICES. (LG)