The introductory physical geology laboratory courses taught at North Carolina State University aims to promote scientific thinking and learning through the use of scientific inquiry-based activities. A rubric describing five possible levels of inquiry was applied to characterize the laboratory activities in the course. Two rock and mineral laboratory classes and a geologic time laboratory class were found to contain a greater proportion of low-level inquiry activities than the other laboratory classes. Student exercises within these classes were modified by increasing the degree of student independence, exploration, and prediction required for several activities. Such modifications included students categorizing rock samples before instruction on rock types and predicting the placement of fossils along a geologic time line. Learning gains were measured and compared between students in the traditional lower-inquiry (control) and the revised higher-inquiry laboratory classes (treatment). In all three classes, the increase in inquiry level was found to positively influence student academic performance on postlaboratory assessments and related exam questions.