MILA-S is an interactive open learning environment for scientific modeling (Joyner, Goel, & Papin, 2014). It enables
students to build conceptual models of ecological phenomena, evaluate them through simulation, and revise the models
as needed. MILA-S automatically spawns simulations from the conceptual models, making modeling easier for the student. Earlier work had described the use of MILA-S in middle school. In this paper, we report an experiment on the use of MILA-S in two college-level classes. In one class, we found that almost half of the students showed improved understanding of scientific modeling; in the other class, about two thirds of the students showed enhanced understanding.