This study analyzes longitudinal data from 17 four-year institutions in the United States to determine how the distinctive instructional and learning environment of American liberal arts colleges accounts for the positive impact of liberal arts college attendance on four-year growth in critical thinking skills and need for cognition. We find that, net of important confounding influences, attending an American liberal arts college (vs. a research university or a regional institution in the United States) increases one's overall exposure to clear and organized classroom instruction and enhances one's use of deep approaches to learning. In turn, clear and organized classroom instruction and deep approaches to learning tend to facilitate growth in both critical thinking and need for cognition--thus indirectly transmitting the impact of attending a liberal arts college.