I ran across this from Koeno Gravemeijer, quoted by Jeffrey Choppin in the Mathematics Education Research Journal:
Older design principles take as their point of departure the sophisticated knowledge and strategies of experts to construe learning hierarchies… The result is a series of learning objectives that can make sense from the perspective of the expert, but not necessarily from the perspective of the learner.
This is where I have struggled with the Common Core State Standards. That business about complex fractions last spring? This is what I was talking about. My recent fussiness with Hung-Hsi Wu? Ditto. Even that business about logs and quotients; it was about the difference between the views of mathematics content seen by experts and by novices.