"With podcasting gaining more mainstream adoption in higher education, it’s critical to examine its effectiveness in improving the student learning experience. To this end, this paper examines the effectiveness of podcasts integrated into the curriculum (PIC) versus podcasts as supplemental material (PSM). Considering recent empirical work on the effectiveness of podcasting, this study collected data from students enrolled in lower level and upper level language courses. Results revealed an inconclusive relationship among PIC students’ learning outcomes (as measured by their final grades). In contrast, however, our findings indicate a strong relationship between the use of PSM and students’ final grades, particularly in upper level courses."
Academic effectiveness of podcasting: A comparative study of integrated versus supplemental use of podcasting in second language classes. (2012) Computers & Education 58 (1): 43-52 doi:10.1016/j.compedu.2011.08.021
So basically, listening to podcasts on your own time is a measure of engagement, which correlates with outcomes (as does reading, revision, and getting an early night). PIC ... not so much. The jury is still out on the value of podcasts.