The inevitable responses to high stakes testing, wherein students' test scores are highly consequential for teachers and administrators, include cheating, excessive test preparation, changes in test scoring and other forms of gaming to ensure that test scores appear high. Over the last decade this has been demonstrated convincingly in the USA, but examples in Great Britain abound. Yet the most pernicious response to high stakes testing is perhaps the most rational, namely, curriculum narrowing. In this way more of what is believed to be on the test is taught. Curriculum narrowing, however, reduces many students' chances of being thought talented in school and results in a restriction in the creative and enjoyable activities engaged in by teachers and students. The tests commonly used with narrower curricula also appear to restrict thinking skills. In addition, responses to high stakes environments can easily retard the development of achievement in later grades as a function of the restrictions on learning in earlier grades. Finally, narrowing compromises interpretations of construct validity. The dominance of testing as part of American and British school reform policies insures that many of the skills thought to be most useful in the twenty-first century will not be taught. Thus students and their national economies will suffer when nations rely too heavily on high stakes testing to improve their schools. (Contains 5 tables.)