With the current concern over the growing need for more engineers, there is an immediate need to improve freshman engineering retention. A working model for freshman engineering retention is needed. This paper proposes such a model based on Tinto's Interactionalist Theory. Emphasis in this model is placed on pre-college characteristics as predictors for student academic success and retention. Through a literature search of both engineering education and general empirical studies, a list of significant pre-college characteristics important for modeling freshman engineering student success and retention was developed. Significant differences were found between the engineering education and general empirical studies. The final model is described in terms of a block diagram with an extension to statistical modeling. Tables of empirical studies that have included pre-college characteristics as predictors for student success and retention are included. An application using data from a University of Michigan study is discussed.