Laboratory sections of university Earth science courses provide hands-on, inquiry-based activities for students in support of lecture and discussion. Here, I compare student conceptual knowledge outcomes of laboratory sections by administering an independent concept inventory at the beginning and end of two courses: one that had a lecture and a laboratory section, and one that had only a lecture. Students in both courses demonstrated a significant increase in inventory scores over the course of the semester. The mean increase in score for the course with a laboratory was 33% greater (43% greater for matched-identification score analysis) than for the lecture-only course. One notable difference between the two courses was that the course without the lab was also a time-shortened course, while the course with a lab spanned a full, traditional-length academic term. Because a great deal of research exists demonstrating that time-shortened, intensive university courses produce the same increase in student concept knowledge as traditional-length courses, the inclusion of the laboratory section most likely led to the greater student learning gains in the full-length course. This study demonstrates the importance of having a laboratory component of an introductory-level, university Earth science course.