That is, if what is meant by "demanding curriculum" is making students memorize a lot of insignificant and cognitively isolated minutiae, such as names of places and things, dates, tables, graphs & charts, differences between, similarities and characteristics of, explanations about, describing attributes of, steps in the sequences, and, above all, what students think the teacher thinks they should write down on their papers to earn their points.
I simply cannot take the "more information learned in isolation is BETTER for students because MORE is CHALLENGING" perspective on curriculum any longer. I cannot take it because I cannot abide anything that is not good for students. And this isn't good for kids. It's downright wrong. It fundamentally disrespects students, because it tells them we think they're incapable of using their brains, so we'll do the work for them and fill their heads with supposedly useful knowledge.
It is an attitude that must change, especially when we are trying to prepare students for their future 21st century world, not our world of the past, or even the present.
You see, the information we strive so hard to fill their heads with is just a Google search away. Google has made traditional teaching obsolete.
Who cares if they can draw the graph of how enzymes lower the activation energy of biochemical reactions? I care more about how, if presented with that graph, they can draw conclusions from it, and then generate authentic questions to test.
Who cares if they can name all of the animal phyla without looking, and name an example of an animal in each of those phyla? I'm more interested if students can see patterns of evolutionary change and similarities amongst all of the phyla and their various representatives.
Who cares if they know all of the in-depth scientific terms associated with mitosis, such as kinetochore & microtubule? I'm way more concerned with the fact that, after they have studied the process (via Google and the plethora of online animations), they can make predictions based on that knowledge that will lead them to deduce and investigate the causes of cancer.
I'm much more interested in using an essential, focused curriculum to improve my students' thinking skills. Not to improve their knowledge of what I consider trivia.
Curriculum, you see, should be used as a vehicle through which student thinking skills are honed and improved. A demanding curriculum is one that pushes students to think at higher levels--not one that encourages them to memorize more random facts they will soon forget.
Because, honestly--if students don't remember what you've taught them, you've just wasted everyone's time.