We've moved to the Common Core State Standards because the world is not the same as it was in the 1950s, 60s, or even just a few years ago. Jobs are different, college is different and our schools must be different.
We have to teach in a completely new way, focused on mastering skills and working through problems instead of rote memorization. Our standards have to be more rigorous and our expectations higher if our students are ever going to be able to compete in a global society.
The old standards were like a thorough to-do list where each standard was an item waiting to be accomplished. They were taught, tested, and crossed off the list.
Common Core is more like a spiral staircase where each step is a standard, such as dividing multi-digit numbers. When a student masters it, she moves on to the next step. But she doesn't leave the old standard behind; it's still there supporting her as she stands on the next step. Each new skill builds on the skills and foundations that came before.