THE SEARCH FOR QUANTITATIVE MEASURES IN SENTENCE STRUCTURES THAT ARE SIGNIFICANT INDICATORS OF CHRONOLOGICAL AND MENTAL MATURITY IN SCHOOL CHILDREN WAS THE PURPOSE OF THIS STUDY. COMPARISONS WERE MADE OF COMPOSITIONS WRITTEN BY STUDENTS OF SUPERIOR IQ AT THE SAME GRADE LEVELS. THIS PART OF THE PROJECT HAD TWO OBJECTIVES--(1) TO SEE WHETHER SUPERIOR STUDENTS NEAR THE BEGINNING OF THEIR WRITING CAREERS ARE ALREADY MEASURABLY AHEAD OF THE AVERAGE STUDENTS IN SYNTACTIC MATURITY, AND IF SO IN WHAT RESPECTS, AND (2) TO DETERMINE WHETHER SUPERIOR STUDENTS NEAR THE END OF THEIR PUBLIC SCHOOL TRAINING ARE FURTHER AHEAD OF THEIR AVERAGE COUNTERPARTS. ANOTHER COMPARATIVE EXERCISE WAS CONDUCTED BETWEEN THE SYNTACTIC WRITTEN STRUCTURES OF SUPERIOR AND AVERAGE TWELFTH-GRADERS WITH THOSE OF SKILLED ADULTS PUBLISHED IN "HARPERS" AND "ATLANTIC" MAGAZINES. THIS SECOND PROJECT TASK WAS CONDUCTED TO DETERMINE WHETHER TWELFTH GRADERS (AT LEAST SUPERIOR ONES) HAVE ALREADY ATTAINED FULL SYNTACTIC MATURITY OR WHETHER, INSTEAD, SKILLED ADULT WRITERS ARE AHEAD OF THEM, AND IF SO, IN WHAT RESPECTS. IN GENERAL, THE RESULTS OF THE STUDY SHOWED DEFINITE DEVELOPMENTAL TENDENCIES OCCURRING BETWEEN GRADES 4 AND 12 AND CARRYING EVEN FARTHER IN THE WORK OF SKILLED ADULTS. THUS, THE MEASURES EMPLOYED WERE DEEMED SUFFICIENTLY SENSITIVE TO DETECT MENTAL, AS WELL AS CHRONOLOGICAL, MATURITY. THE STUDY WAS AN EXTENSION OF COOPERATIVE RESEARCH PROJECT 1998, ENTITLED "DIFFERENCES IN GRAMMATICAL STRUCTURES WRITTEN AT THREE GRADE LEVELS." (JH)