The level of thinking that is characteristic of the typical college freshman and the skills needed by college science courses are addressed, and the Development of Reasoning in Science project (Project DORIS) at California State University, Fullerton, is described. While the typical college freshman functions at the concrete level of thinking, many college science professors assume that students are capable of functioning at the formal operational level. Project DORIS, a course in abstract thinking for college science majors, focuses on the following thinking skills: combinatorial logic, correlation, hypothetical-deductive reasoning, isolation and control of variables, and proportional reasoning. First-year offerings in the sciences present concepts that can be taught with both concrete and formal thought processes. The teaching strategy incorporates exploration, invention, and discovery activities and enables the learner to use logic based on experience. As the student develops the reasoning skills associated with concrete thinking processes, the sequencing moves to a higher level with the objective of enhancing intellectual growth. Sample learning experiences from the various science content areas are described, along with the evaluation design for the project. (SW)