An extensive, internally cross-validated analytical study using nested (within academic disciplines) Multilevel Modeling (MLM) on 4,560 students identified functional criteria for defining high school curriculum rigor and further determined which measures could best be used to help guide decision making for marginal applicants. The key outcome used in MLM analyses was a composite variable including first year GPA and hours completed per term, which proved to relate well with predictors. Consistent findings guided the design of a Criteria Decision Matrix and a set of advising tools that has been shared with and well received by Florida high school guidance counselors. A preliminary scan of bivariate relationships between some 35 possible predictors and outcome variables (USF GPA and Hours Earned) suggested that once high school GPA was entered into a regression model (MLM), few other variables would contribute much variance prediction. Nonetheless, some politically sensitive variables were included in the MLM analyses: sex, race/ethnicity and low-income target schools. As expected, in the cross-validated MLM analyses, high school GPA was by far the strongest predictor, with AP courses, dual enrollment courses, number of STEM units, number of language units also exhibiting some importance. Test scores were worthless and, in fact contributed negatively to prediction of first year GPA. Further analyses identified four key Rigor Criteria that related strongly with first year performance: (1) Taking an AP course (not passing); (2) Taking a dual enrollment course; (3) Taking more than minimum required STEM courses (Science, Technology, Engineering, Math); and (4) Taking more than minimum required language courses (English and Foreign Languages). Having two or more of the Rigor Criteria proved highly effective in predicting USF performance. This was combined with high school GPA to create a matrix of automatically admit, automatically deny and consider further. This has substantially reduced the time and effort required by the admissions office. Note that among students with a 4.0 or higher high school GPA who had none of the Rigor Criteria, 83% earned a USF GPA below 2.0, this dropped to about 10% for those having two, and to 2% for those having three or more of the Rigor Criteria. All lines relating to these criteria were monotonic, providing strong evidence of their validity. (Contains 3 footnotes, 3 figures, and 5 tables.)