Interactive Web-based tutorials were developed as a supplement to lectures in an introductory statistics class. A quasi-experimental design compared learning outcomes of students who attended one of two classes that offered the tutorials to students as an extra-credit course option to those who attended a lecture-only class. Analysis of critical items on five course exams revealed that students who attended the classes with tutorials scored higher on four out of five topics covered by the tutorials than students who attended the lecture-only class. Tutorial use leading to mastery of the concepts was associated with exam performance on the critical items. These findings suggest that Web-based tutorials can be an effective supplement to class lectures for enhancing student learning.