So, they're called the Next Generation Science Standards but are they really standards in the same sense that we're used to? Throw in there that the assessable units are called performance expectations (PEs) and I'm not so sure where we stand anymore. And I don't think I'm alone either, judging by a post from Brian MacNevin in the Google+ NGSS Peer Learning Network.
I believe that the disequilibrium exists because performance expectations are NOT the same thing as standards. PEs represent what students should be able to do at the end of instruction. They give us an indication about what could be assessed formally...whenever we get to that point in the implementation process. They're helpful for us to know the level of rigor that we need to bring to our instruction, curriculum and assessment. We need to closely examine the PEs and they should guide our instruction. So, I agree with NSTA and Dr. Bybee in that regard.
The PEs do not have to necessarily be the end targets of instruction though. I'm working on a unit right now using a group of PEs (MS-PS2-2, MS-PS3-1, MS-PS3-2, MS-ETS1-2, and MS-ETS1-4). I'm using the disciplinary core ideas, cross-cutting concepts and science & engineering practices to guide instruction. So, students will plan investigations, explore stability & change, etc. throughout the unit. But I'm not limiting myself to a final target of planning an investigation only relating to force and mass as indicated by MS-PS2-2. I think assessing and teaching ONLY the PEs is short-sighted. So, in that regard I agree with Achieve.
So, in the unit I'm planning my summative assessment is two-fold:
1) An interactive assessment using an Explore Learning gizmo (Roller Coaster Physics) that requires students to answer questions related to forces and energy using the gizmo and to plan and conduct a mini investigation, of their choice etc.
2) An engineering project that requires students to construct a catapult and maximize the energy transferred to a projectile. (Note: This builds off a previous unit of study in math class where they construct and calibrate a catapult.)
In short, the PE's guide our instruction but we are not limited to them as the target of instruction as we might be with standards. Is that any clearer? Probably not...but we're all works in progress as we grapple with the NGSS and what they mean for how we do business in science education.