The academic momentum perspective suggests that the speed with which undergraduates initially progress in college significantly affects their likelihood of completing a degree, an effect separate from those of high school academic preparation and family socioeconomic status. Growth curve modeling of undergraduate transcript data reveals that the number of credits attempted in the first semester of college sets a trajectory that influences later chances of degree completion. Several techniques addressing selection bias indicate that delay between high school and starting college, and also attempting a low course load in the first semester (part-time attendance), are associated with lower degree completion, while attending summer school after freshman year is associated with significantly better graduation chances. In sum, the central claims of momentum theory are supported. (Contains 6 tables and 1 figure.)