Our study used a natural experiment to compare a project-based cornerstone course with the traditionally-taught introductory course in civil engineering. During the study, two sections of the course were organized around an overarching project, the design of an event center, and the remaining sections used guest lectures, a textbook, and traditional laboratory activities to familiarize students with civil engineering. Students in the project-based course gained more on measures of creativity and design self-efficacy on a survey of engineering identity than traditionally-taught students. Pre/post comparisons of the project-based students confirmed gains in design self-efficacy, but indicated a decrease in mathematical self-efficacy. In interviews students indicated that they recognized and appreciated that the project-based course enabled them to do real engineering, speaking to the development of engineering identity. They expressed concerns, however, that they might not be learning de-contextualized science and mathematics, a possible explanation for the decrease in mathematics efficacy.