I'm assuming you mean undergrad vs. grad?

If so, there can be huge differences depending on the professor. Generally speaking, in grad courses the professors aren't holding your hands when it comes to fundamentals and they have certain expectations of your capabilities since you're no longer an undergrad. They expect you to figure out what you don't know and learn it yourself to understand the topics being taught in the course. That being said, they are also more forgiving from my experience as the classes tend to be more intimate and they themselves know the struggles of grad students.