In large lecture courses, it can be challenging for instructors to address student misconceptions, supplement background knowledge, and identify ways to motivate the various interests of all students during the allotted class time. Instructors can harness instructional technology such as screencasts, recordings that capture audio narration along with computer screen images, to supplement the lecture with content that addresses the diversity in student academic backgrounds, motivations, and interests, to extend the classroom experience, and reach the individualized needs of students. This study documents the strategic use of screencasts in a large introductory Materials Science and Engineering (MSE) course, and examines their impact on student usage and course performance. To assess the efficacy of screencasts, students were surveyed to determine how they used screencasts and whether they perceived these resources to be helpful. In addition, we correlated student usage based on website hits with student performance (e.g. final grade) to determine statistical significance. Since the course is comprised of students from different academic and social backgrounds, we also analyzed usage and performance patterns for particular student subgroups. The results indicate that students perceive the screencasts to be helpful and tend to use the resources as a study supplement. Overall, usage of screencasting in its various forms is positively and significantly correlated with course performance as indicated by the final grade. The most substantial gains were found for students with the least amount of prior exposure to concepts in the course material. These results indicate a potential for screencasts to address the various academic needs of students in a large lecture environment.