BASED ON EMPIRICAL DATA ACCUMULATED FROM TWELVE JUNIOR COLLEGES UNDER THE 2-SEMESTER CALENDAR, THE MODEL DEVELOPED IN THIS STUDY CAN BE USEFUL IN PREDICTING CHANGES IN PLANT USE UNDER THE 4-QUARTER CALENDAR. THIS CALENDAR REVISION HAS FOUR CONSTRAINTS--(1) THE SENIOR INSTITUTIONS IN THE STATE HAVE ADOPTED IT, (2) THE STUDENT'S CHOICE OF QUARTER IN WHICH TO ENROLL CAN NOT BE CONTROLLED, (3) FEEDER HIGH SCHOOLS GENERALLY FOLLOW THE JUNE GRADUATION PATTERN, MAKING ARTICULATION OF TERMS DIFFICULT, AND (4) JUNIOR COLLEGE STUDENTS HAVE A HIGH-ATTRITION AND LOW-PERSISTENCE CHARACTERISTIC. WITHIN THESE PARAMETERS, THE MODEL PROVIDES A COMPARISON OF PLANT USE UNDER VARIOUS ENROLLMENT PATTERNS AND VARYING PROPORTIONS OF STUDENTS ELECTING YEAR-ROUND ATTENDANCE. THE MODEL CAN ALSO BE USED TO EXAMINE SUBPOPULATIONS (E.G., BY SEX AND BY SCHOLASTIC ABILITY) AND TO COMPUTE THEIR EFFECTS ON FACILITY USE. THE EVIDENCE ALSO INDICATES THAT, AS PART OF THIS PREDICTIVE STUDY, FURTHER RESEARCH IS NEEDED ON THE CHARACTERISTICS OF COLLEGES AS THEY RELATE TO EACH OTHER AND TO THEIR COMMUNITIES, AND ON THE RELATIVE APTITUDES OF MEN AND WOMEN STUDENTS IN URBAN COLLEGES. THE COMPUTATIONS ARE ILLUSTRATED BY GRAPHS AND CHARTS. (HH)