This paper estimates a dynamic model of college enrollment, progression, and graduation. A central feature of the model is student effort, which has a direct effect on class completion and an indirect effect mitigating risks on class completion and college persistence. The estimated model matches rich administrative data for a representative cohort of college students in Colombia. Estimates indicate that effort has a much greater impact than ability on class completion. Failing to consider effort as an input to class completion leads to overestimating ability's role by a factor of two or three. It also promotes tuition discounts based on a pre-determined student trait--ability--rather than effort, which can be affected through policy, thus limiting higher education's potential for social mobility.