Constructivist learning theory holds that "learning consists less in recording information than in interpreting it. To interpret what is received and is attended to, the learner must personally construct meaning for it." Unfortunately, opportunities for interpreting conceptual information are often lacking in classroom environments--particularly in the area of biological science. By contrast, constructivist environments in science are created by learning experiences that are "active, hands-on, lab-rich, curricularly lean, connected to contexts, and enmeshed in a community of learners." Field-based learning provides an ideal environment for constructivist learning that promotes deep scientific understanding in conservation biology and biodiversity. The "Field Course Experiential Learning Model" evolved from repeated short-term study abroad field course experiences in selected biomes from around the world over a six-year period. This paper reports assessment findings from three cohorts of students participating in a short-term study abroad field course experience in Costa Rica, entitled Environmental Science and Conservation Biology: A Field Study in the Biodiversity of Costa Rica, using the "Field Course Experiential Learning Model" as its pedagogical framework. It describes cognitive and affective learning gains of students participating in the course. (Contains 2 figures and 3 tables.)