Each student arrives to a classroom with a completely different set of experiences and a varied understanding of the topic to be discussed. Because of this, I typically require my students to arrive to class having done a pre-class preparatory assignment. This is typically a 10-30 minute assignment where students might have to read or watch a video. Students might have to reflect on their reading, or attempt to solve some problem, but aren't expected to have the "correct" answer.
The purpose of pre-class prep is to prime students to be ready to engage in the topic when they arrive to class. If students have already been exposed to the material and have already had time to think about the topics, then when we engage with them in class, they are more likely to be able to retain what they learn.
My goal, always, is to provide high-quality learning environments.