The No Child Left Behind Act of 2001 (NCLB) was a 2002 United States Act of Congress promoted by the presidential administration of George W. Bush. It reauthorized the Elementary and Secondary Education Act and included Title I provisions applying to disadvantaged students. It mandated standards-based education reform based on the premise that setting high standards and establishing measurable goals could improve individual outcomes in education. To receive school funding from the federal government, U.S. states had to create and give assessments to all students at select grade levels.

The act did not set national achievement standards. Instead, each state developed its own standards. NCLB expanded the federal role in public education through further emphasis on annual testing, annual academic progress, report cards, and teacher qualifications, as well as significant changes in funding. While the bill faced challenges from both Democratic Party and Republican Party politicians, it passed in both chambers of the U.S. Congress with significant bipartisan support.

Many of its provisions were highly controversial. By 2015, bipartisan criticism had increased so much that a bipartisan Congress stripped away the national features of NCLB. Its replacement, the Every Student Succeeds Act, turned the remnants over to state governments.

Prior to the No Child Left Behind Act of 2001, the Elementary and Secondary Education Act (ESEA) was signed into law by President Lyndon B. Johnson in 1965. Its goal was to provide additional resources to low-income students, but following its enactment, the nation repeatedly fell short of meeting the law's goal of providing full educational opportunities to students. Fears concerning the American education system culminated with the 1983 release of a report entitled A Nation at Risk, written by President Ronald Reagan's National Commission on Excellence in Education. This report suggested that America's economic security would be severely compromised unless there were a reorientation of the education system and an increase in the set of academic standards that students were expected to achieve. Though many Republican groups historically opposed the active role of the federal government in education, lobbying efforts, public opinion, and other political developments in Washington (such as the Republican defeat in the 1996 presidential election) caused congressional Republicans to push for federal educational reforms that emphasized standardized testing and other accountability measures. At the time, increased attention was being paid to the state of education in the nation because prior to the 2000 presidential election, then-candidate George W. Bush made a number of campaign promises related to bipartisan education reform.

The increased focus in the U.S. on educational standards and accountability reflected international education policy developments and debates. After World War II, international organizations such as the United Nations Educational, Scientific and Cultural Organization (UNESCO), the World Bank, and the Organisation for Economic Co-operation and Development (OECD) devoted their attention to global educational development. From the 1960s onward, these organizations increasingly focused on learning outcomes and evaluation procedures that included the evaluation of education systems against defined standards of performance. The 2001 NCLB Act was part of this global movement toward greater accountability in education.

President George W. Bush first proposed the use of federal aid to create a plan by which to hold schools accountable for the educational outcomes of their students on January 23, 2001; however, as it was initially described, the Act faced significant criticism from interest groups such as the Education Trust because of its inclusion of vouchers. Vouchers would enable parents to choose a different school (public, private, or otherwise) for their child to attend if their district failed to meet state standards; however, critics stated that this move would take funds away from schools that needed the most funding. The NCLB Act was introduced in the U.S. House of Representatives on March 22, 2001, and it was coauthored by the representatives John Boehner, George Miller, and the senators Ted Kennedy and Judd Gregg. As it made its way through the House of Representatives and the Senate, the bill faced a number of challenges, ranging from Democratic appeals for more funding, to Republican pushback on the increased role of the federal government in the realm of education. Despite this, the Act garnered bipartisan support in both chambers of the legislature, and it was passed in the House of Representatives on December 13, 2001 (voting 381–41), and in the U.S. Senate on December 18, 2001 (voting 87–10). It was signed into law by Bush on January 8, 2002.

According to the Department of Education, the No Child Left Behind Act of 2001 aimed to increase school accountability for student educational outcomes and reduce disparities between lower-performing and higher-performing students and districts. To achieve these goals, the NCLB Act required all federally funded public schools to administer a standardized test annually to students in selected grades. To improve student outcomes, the act identified several strategies school districts could employ, such as teacher professional development, educational technology, and activities to involve parents. The act also required each local agency to determine the average number of students in daily attendance in the K-12 schools it served to allocate grant money effectively for NCLB programs. Additionally, the law emphasized improving the communication of information about student achievement and school performance to parents through reporting systems designed to reflect best educational practices.

Schools that receive Title I funding through the Elementary and Secondary Education Act of 1965 must make Adequate Yearly Progress (AYP) in test scores (e.g. each year, fifth graders must do better on standardized tests than the previous year's fifth graders).