Unless you’ve been living in a cave you know that since 2009 more than 20 states have made significant changes to their teacher or principal evaluation systems. In a new analysis out today Bellwether takes a deeper look at 21 of them along a set of common dimensions. This builds on the smaller analysis of high-profile states we released last year. Some big stories embedded in all this – questions about how the moving parts all fit together, for instance many states have new evaluation policies but still use “last in/first out” for layoffs. And big implementation challenges.