For all the fractious debate in America over the state of public schools, those on the political Left and Right agree that the "achievement gaps" are real. But what do most people mean when they say "achievement gaps"? Gaps in standardized test scores, of course. The gaps consist of the differences between the test scores of students of color and those of white students and between the scores of poor children and those of their wealthier peers. Referring to those test score gaps as achievement gaps naturally implies acceptance of the tests as valid measures of student knowledge and skills. The author maintains that the perceived academic achievement gaps might actually reflect differences in students' abilities (or willingness) to behave in idiosyncratic ways while taking standardized tests--ways unconnected to content knowledge or to "general aptitude." He calls such student testing behaviors TestThink. In the context of what he calls the "No Child Left Untested" environment, the author reexamines this notion. (Contains 1 figure and 3 notes.)