I have a group that watches the videos the night before and then uses class time (extremely effectively, I might add) to work through challenge problems, labs, quizzes, and projects. In the same class, I have two students that work 30-35 hours each week outside of school. They use the class time to watch the videos together and then move forward. They rarely do chemistry at home, which is fine with me. Yet a third group does most of their chemistry at home, checks with me in class, and then moves on to geometry for the rest of the period. Each group is totally different than the others, but they are still learning.