The United States education system depends on legislation and funding at the federal, state and local levels. Public understanding of assessment therefore is important to educational reform in the USA. Educational reformers often invoke assessment information as a reason for reform, typically by citing unacceptable achievement on some measure or indicator. Recent educational reforms in the US also rely on assessment information as evidence of the effectiveness of the reform, designing some sort of accountability system into the reform. Public opinion about testing in three recent waves of US educational reform (the minimum competency movement in the 1970s, the standards-based reform movement in the 1980s and 1990s, and the No Child Left Behind era beginning in 2002) shows two themes. One is public belief in the objectivity of testing. The other is public belief in using tests data comparatively and competitively. (Contains 2 tables and 1 figure.)