A CROSS-CULTURAL STUDY WAS CONDUCTED TO COMPARE THE ACHIEVEMENT LEVELS OF BRITISH AND UNITED STATES ELEMENTARY SCHOOL STUDENTS IN GRADES 1-6, OF VARYING ABILITY LEVELS, FROM BOTH PRIVATE AND PUBLIC SCHOOLS AT THE APPROXIMATE BEGINNING, MIDDLE, AND END OF THE ACADEMIC YEAR. ACHIEVEMENT ANALYSES WERE BASED PRIMARILY UPON SCORES EARNED ON THE CALIFORNIA ACHIEVEMENT TEST, MODIFIED TO ELIMINATE CULTURALLY BIASED ITEMS. BRITISH-CONSTRUCTED, STANDARDIZED ACHIEVEMENT TESTS WERE USED PRIMARILY AS MEASURES OF THE VALIDITY OF THE CALIFORNIA ACHIEVEMENT TEST. VALIDITY COEFFICIENTS BETWEEN BOTH TESTS ON COMPARABLE SUBJECT-MATTER AREAS RANGED FROM 0.56 TO 0.89. SEVEN CONCLUSIONS WERE REACHED--(1) THROUGH THE FIRST FOUR GRADES, BRITISH PUPILS WERE AT HIGHER LEVELS OF ACHIEVEMENT IN NEARLY ALL SUBJECT AREAS AND ACROSS ABILITY LEVELS, (2) BY GRADES FIVE AND SIX, U.S. PUPILS WERE ACHIEVING AT APPROXIMATELY THE SAME LEVELS IN NEARLY ALL THE TESTED SUBJECT AREAS, (3) ON A COMPARATIVE BASIS, BRITISH PUPILS WERE STRONGEST IN ARITHMETIC FUNDAMENTALS AND U.S. PUPILS IN ENGLISH USAGE, (4) U.S. PUPILS SCORED COMPARATIVELY HIGHER ON U.S. TESTS, BRITISH ON BRITISH TESTS, (5) THE MARGIN BETWEEN HIGH AND AVERAGE ABILITY GROUPINGS WAS GREATER FOR THE BRITISH SAMPLE, (6) THERE APPEARED TO BE LITTLE DIFFERENCE BETWEEN THE ACHIEVEMENT OF PUBLIC AND PRIVATE SCHOOL PUPILS, AND (7) U.S. PUPILS WERE STRONGEST IN REASONING PROBLEMS, WHILE BRITISH PUPILS WERE STRONGEST ON METHOD PROBLEMS. (HB)