In science, statisticians must frequently grapple with interaction effects. Let's say, for example, that a scientist wants to study the impact of diet and exercise on lowering cholesterol. They have one group follow a low-fat diet, another a new running regimen, and a third group both. It's possible that both the diet group and the exercise group see a modest dip in cholesterol. But it's also possible that the third group will see a drop that is more than double what could have been achieved by diet or exercise alone?meaning that diet and exercise are ?interacting? in some way to affect cholesterol more powerfully. But, at what levels do participants see this interaction effect? When you follow a strict diet and exercise once a week? Twice? Etc.
In education, interaction effects are everywhere. As I've argued before, a strong curriculum implemented by skilled instructor often yields amazing results. The same curriculum implemented by a weak teacher may yield no (or negative) student achievement gains. That's because, as anyone who's ever worked in a school knows, outstanding student achievement results are the product of many different interacting elements within schools, not just of standards or curriculum alone.
For policy makers, it's challenging because no policy can control all of the (school-based) factors that will determine whether their programs succeed or fail in boosting student achievement.
So it is with Common Core. While the standards themselves are far more rigorous than what existed in most states previously,...