Presents a model for predicting the effects of alternative federal policies for student financial aid on postsecondary enrollment rates and patterns. The model is used to explore the effects of 10 Basic Educational Opportunity Grant aid rules currently under consideration. The rules apparently would stimulate 3 to 5 percent increases in the numbers of high school graduates going on to public and private colleges and universities--about 40 to 60 thousand more a year. The study ranks the 10 policies according to their effectiveness in stimulating enrollment at various types of institutions among sample students categorized by sex, race, family income, and ability. The strongest responses are to be found among women (both white and nonwhite), low-income students, and students in the lowest and middle quartiles of the ability distribution. 74 pp. Ref.