It should be emphasized that the curriculum isn't mandated by the Common Core. It's up to the districts to decide how to implement it. So the actual work and the way it's presented is often due to the all-too-human desire for the sure thing. Many vendors have popped up as being "core aligned." They just vendors. It's the districts that decide to buy a program and implement it. So there's nothing in the common core that dictates exactly how something should be taught, only the standards and objectives that are to be met.