For decades we've been studying, experimenting with, and wrangling over different approaches to improving public education, and there's still little consensus on what works, and what to do. The one thing people seem to agree on, however, is that schools need to be held accountable—we need to know whether what they're doing is actually working. But what does that mean in practice?High-stakes tests. Lots of them. And that has become a major problem. Daniel Koretz, one of the nation's...

How do you judge the quality of a school, a district, a teacher, a student? By the test scores, of course. Yet for all the talk, what educational tests can and can’t tell you, and how scores can be misunderstood and misused, remains a mystery to most. The complexities of testing are routinely ignored, either because they are unrecognized, or because they may be—well, complicated.Inspired by a popular Harvard course for students without an extensive mathematics background, Measu...