A study used Alexander Astin's (1993) Input-Environment-Output (I-E-O) model to examine persistence at the United States Coast Guard Academy (Connecticut). Because the study was conducted in a controlled social environment, measures of social environmental influence were derived from multiple inputs, including adaptability polls wherein every student's "fit" was assessed by all others in his organizational unit each semester. Subjects were 619 cadets entering the Academy with the classes of 1991 and 1993; the groups had similar profiles. The research questions addressed the extent to which (1) input variables and academic and social involvement at the end of each of the first four semesters differentiated between persisters and non-persisters; and (2) how input variables related to academic and social integration. Results confirmed the longitudinal nature of the model and the general longitudinal theory of student retention. They also established that the effects of academic and social integration were time-dependent and had their most dramatic impact in the time periods immediately after being received. Results further indicated that the effects of early measures of academic performance and social integration were important indicators of long-term persistence. Additional findings suggest need for further examination of the effects of the required pre-freshman summer program on persistence. Contains 47 references. (MSE)