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K–12 (spoken as "k twelve", "k through twelve", or "k to twelve"), for kindergarten to 12th grade, is an American expression that indicates the range of years of supported primary and secondary education found in the United States, which is similar to publicly supported school grades prior to college in several other countries, such as Afghanistan, Australia, Canada, Ecuador, China, Egypt, India, Iran, the Philippines, South Korea and Turkey.
US Public education was conceived of in the late 18th century. In 1790, Pennsylvania became the first state to require some form of free education for even those who could not afford it. New York passed similar legislation in 1805. In 1820 Massachusetts became the first state to create tuition-free high school, 'Boston English'.
The first K–12 public systems were seen in the early 19th century. In the 1830s and 1840s, Ohioans were taking a significant interest in the idea of public education. Schools commonly operated exclusive of one another at this time in American history, with little attempt at uniformity. The "Akron School Law of 1847" changed this. Named after Akron, Ohio, where the system was first conceived, this law passed by the Ohio legislature largely unified the operations, curriculum and funding of local school systems. Though the law is named "Akron School Law of 1847", it took two years to pass, becoming law in 1849.
"Under the Akron School Law, there was to be one school district encompassing the entire city. Within that district would be a number of elementary schools, with students divided into separate "grades" based on achievement. When enough demand existed, the school board would establish a high school as well. Property taxes would pay for the new school system. A school board, elected by the community, would make decisions about the system's management and hire the necessary professionals to run each school. Illustrating the racism that existed in Ohio during this era, the Akron School Law excluded African-American children from the public school system."
By 1930, all 50 states had passed laws making education compulsory, and in 1965, President Lyndon B. Johnson signed the Elementary and Secondary Education Act (ESEA), granting a large federal expenditure to each state for the purpose of sustaining local K–12 systems. This law essentially enacted K–12 education as the law of the land.
Since its inception, public K–12 has been debated, with several waves of reform throughout the last 50 years. In the 1980s, Reagan's 'A Nation at Risk' initiative provided provisions requiring public education to be evaluated based on standards, and teacher pay to be based on evaluations. In the 1990s, the Goals 2000 Act and the “Improving America’s Schools” act provided additional funding to states to bolster the K–12 systems. This was followed in the 2000s by a rigorous uptick in standards-based evaluations with the No Child Left Behind Act, and the Race to the Top Act. In 2015, President Barack Obama signed the Every Student Succeeds Act (ESSA), giving state government back some individual power over evaluations and standards.
The expression "K-12" is a shortening of kindergarten (K) for 4- to 6-year-olds through twelfth grade (12) for 17- to 19-year-olds, as the first and last grades, respectively, of free education in these countries. The related term "P–12" is also occasionally used in Australia and the United States to refer to the sum of K–12 plus preschool education.
The image at the right is a table that defines the education system in the United States. The table shows the progression of the education system starting with the basic K–12 system then progressing through post-secondary education. K–14 refers to K–12 plus two years of post-secondary where training was received from vocational-technical institutions or community or junior colleges. The K numbers refer to the years of educational attainment and continues to progress upward accordingly depending on the degree being sought.
The term is often used in school website URLs, generally appearing before the country code top-level domain (or in the United States, the state top-level domain). The terms "PK–12", "PreK–12", or "Pre-K–12" are sometimes used to add pre-kindergarten.
In Australia, P–12  is sometimes used in place of K–12, particularly in Queensland, where it is used as an official term in the curriculum framework. P–12 schools serve children for the thirteen years from prep until Year 12, without including the separate kindergarten component. In Canada (Nova Scotia) P–12 is used commonly in place of K–12 and serves students from grade Primary through 12.
K–14 education also includes community colleges (the first two years of university). K–16 education adds a four-year undergraduate university degree. For simplicity purposes education shorthand was created to denote specific education levels of achievement. This shorthand is commonly used in articles, publications and educational legislation. The following list contains the most commonly found shorthand descriptors:
The Career Technical Education (CTE) Unit of the California Community College Economic Development and Workforce Preparation Division focuses on program coordination and advocacy, policy development and coordination with K–18 workforce preparation and career and technical education systems.
The ASCCC Chancellor's Office Career Technical Education (CTE) Unit of the Economic Development and Workforce Preparation Division focuses on program coordination and advocacy, policy development and coordination with K–18 workforce preparation and career and technical education systems. Responsible for the implementation of the Vocational and Technical Education Act (VTEA), managing and coordinating activities that impact other interagency and intra-agency objectives. In addition, the CTE Unit is also responsible for the development, dissemination, and implementation of the California State Plan and the annual performance reports.
Further reference to K–18 education can be found in this publication by Ann Diver-Stamnes and Linda Catelli in chapter 4 "College/University Partnership Projects for Instituting Change and Improvement in K–18 Education".