Book excerpt: 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, Measuring Up demystifies educational testing—from MCAS to SAT to WAIS, with all the alphabet soup in between. Bringing statistical terms down to earth, Daniel Koretz takes readers through the most fundamental issues that arise in educational testing and shows how they apply to some of the most controversial issues in education today, from high-stakes testing to special education. He walks readers through everyday examples to show what tests do well, what their limits are, how easily tests and scores can be oversold or misunderstood, and how they can be used sensibly to help discover how much kids have learned.