INSTRUMENTS PREVIOUSLY DEVELOPED TO MEASURE MENTAL ABILITIES IN WESTERN CULTURES WERE MODIFIED AND USED WITH CHILDREN FROM A WIDER RANGE OF BACKGROUNDS. CHINESE, JEWISH, NEGRO, AND PUERTO RICAN CHILDREN FROM THE FIRST GRADE WERE SELECTED AND DIVIDED INTO 2 SOCIAL GROUPS AND 16 SUBGROUPS. THE TOTAL SAMPLE CONSISTED OF 320 CHILDREN WHO WERE TESTED FOR IDENTIFICATION OF VARYING INTELLIGENCE ABILITIES AND CULTURAL DIFFERENCES. EFFORT AND PERSISTENCE, PERSUASIBILITY, AND AGE WERE CONTROLLED IN THE ANALYSIS OF COVARIANCE DESIGN. THE RESULTS PRODUCED THESE GENERAL CONCLUSIONS - SOCIAL-CLASS AND ETHNIC-GROUP MEMBERSHIP HAVE STRONG EFFECTS ON MENTAL ABILITIES, AND PATTERNS ONCE EMERGED DO NOT ALTER WITHIN GROUPS. (RS)