Hi Emma:
You're right, the selection depends on the topic. In other words, we know what information needs to be taught, Our job then is to decide how best to present it expeditiously so all students can grasp it.
Having extra or back-up exercise can be available so if students are not catching on, we already have an alternative assignment that can be substituted. I thing having more material available than time to present is a good safety factor.
Regards, Barry
