CCR Standards Resources
The site describes itself as "full of free content designed to help educators understand and implement the Common Core and other college and career ready standards." Resources include CCRS-aligned tasks, activities, lessons and more, but also materials to support educators in understanding the standards and the content.
This post from Math with Bad Drawings blog explores the following questions related to the Key Shift of rigor: Do we have a "math ceiling" where some math is beyond our ability to comprehend? If a student can perform the math task I am targeting without conceptual understanding (i.e., they know the procedure, but not why it works), do they really need more?
Author Robert Kaplinsky's accessible explanation addresses what coherence looks like in math instruction.