[ertyuio]

It depends on the teacher first, the class second. For a history/philosophy/social science class, I would assume it very common for the assigned reading to be much more detailed than the in-class discussions, but for the tests to be reading-based. My current history class is taught by a man who loves to be engaged in philosophical, emotional discussions that attack the subject matter at its very core -- but he tends to disregard or, at the very least, mention in passing, the (somewhat important) detailed facts. Then he tests us on the facts. Other teachers of the humanities gave tests that you could pass easily with a fleeting knowledge of the facts.

If your teacher nags you to read, then I highly recommend reading.