This study identified input, environmental, and output variables accounting for differences between successful and unsuccessful groups of underprepared students at Johnson County Community College (Kansas). The study applied an adaptation of Alexander Astin's input-environment-output model of assessing student and institutional effectiveness. "Underprepared" students (n=313) were defined as earning assessment scores resulting in placement in a developmental reading or English course. Successful students (n=188) were defined as those underprepared students who eventually earned a degree or certificate or completed at least 24 credit hours. Two input variables were found to distinguish between the successful and unsuccessful groups: (1) reading scores and reading placement level on the "Assessment of Student Skills for Entry and Transfer" measure and (2) high school grade point average. The only environmental variable separating the groups was the number of first term credit hours. Two output variables, highest developmental English course completed and nondevelopmental grade point average, were also significant factors in separating the two groups. Based on these findings, the completion of reading and English developmental courses appeared of utmost importance in improving the underprepared student's chances for success. Institutional policies that "force" intervention were also viewed as important. Finally, mandatory placement in developmental courses during the first semester of enrollment seemed vital to helping underprepared students succeed. (Contains 20 references.) (GLR)