In this paper, we tell a story of iterative design and continual improvement of an asynchronous technological resource, pencasts, to support development of students' modeling skills while studying at home. Our students were typically engineering majors, enrolled in differential equations as a prerequisite for their subsequent engineering courses. The course used a modeling-first approach to teaching the differential equations content. In this paper, we share four aspects of the students' reactions to the pencasts: the students' self-assessments of the helpfulness of the pencasts, how they used pencasts, why the students chose (not) to use them, and the relationship between pencast usage and achievement.