Schooling is compulsory for all children in the United States, but the age range for which school attendance is required varies from state to state. Most children begin elementary education with kindergarten (usually five to six years old) and finish secondary education with twelfth grade (usually eighteen years old). In some cases, pupils may be promoted beyond the next regular grade. Some states allow students to leave school between 14–17 with parental permission, before finishing high school; other states require students to stay in school until age 18. 19] Educational attainment in the United States, Age 25 and Over (2009) EducationPercentage High school graduate86. 68% Some college55. 60% Associates and/or Bachelor’s degree38. 54% Bachelor’s degree29. 0% Master’s degree7. 62% Doctorate or professional degree2. 94% Most parents send their children to either a public or private institution. According to government data, one-tenth of students are enrolled in private schools. Approximately 85% of students enter the public schools, largely because they are tax-subsidized (tax burdens by school districts vary from area to area).School districts are usually separate from other local jurisdictions, with independent officials and budgets. There are more than 14,000 school districts in the country.  More than $500 billion is spent each year on public primary and secondary education.  Most states require that their school districts within the state teach for 180 days a year.  Parents may also choose to educate their own children at home; 1. 7% of children are educated in this manner.  Nearly 6. million students between the ages of 16 and 24 in 2007 dropped out of high school, including nearly three of 10 Hispanics.  The issue of high-school drop-outs is considered important to address as the incarceration rate for African-American male high school dropouts is about 50 (fifty) times the national average.  In 1971, the Supreme Court ruled unanimously that forced busing of students may be ordered to achieve racial desegregation.  This ruling resulted in a white flight from the inner cities which largely diluted the intent of the order.This flight had other, non-educational ramifications as well. Integration took place in most schools though de facto segregation often determined the composition of the student body. By the 1990s, most areas of the country have been released from mandatory busing. In 2010, there were 3,823,142 teachers in public, charter, private, and Catholic elementary and secondary schools. They taught a total of 55,203,000 students, who attended one of 132,656 schools.  States do not require reporting from their school districts to allow analysis of efficiency of return on investment.The Center for American Progress commends Florida and Texas as the only two states that provide annual school-level productivity evaluations which report to the public how well school funds are being spent at the local level. This allows for comparison of school districts within a state.  In 2010, American students rank 17th in the world. The Organisation for Economic Co-operation and Development says that this is due to focusing on the low end of performers. All of the recent gains have been made, deliberately, at the low end of the socioeconomic scale and among the lowest achievers.The country has been outrun, the study says, by other nations because the US has not done enough to encourage the highest achievers.  About half of the states encourage schools to recite the Pledge of Allegiance to the flag.  Teachers worked from about 35 to 46 hours a week, in a survey taken in 1993.  In 2011, American teachers worked 1,097 hours in the classroom, the most for any industrialized nation measured by the Organisation for Economic Co-operation and Development. They spend 1,913 hours a year on their work, just below the national average of 1,932 hours for all workers. 33] In 2011, the average annual salary of a preK-12 teacher was $55,040.  Transporting students to and from school is a major concern for most school districts. School buses provide the largest mass transit program in the country, 8. 8 billion trips per year. Non-school transit buses give 5. 2 billion trips annually. 440,000 yellow school buses carry over 24 million students to and from schools.  School start times are computed with busing in mind. There are often three start times: for elementary, for middle/junior high, and for high school.One school district computed its cost per bus (without the driver) at $20,575 annually. It assumed a model where the average driver drove 80 miles per day. A driver was presumed to cost $. 62 per mile (1. 6 km). Elementary schools started at 7:30, middle schools/junior high school started at 8:15 and senior high schools at 9:00. While elementary school started earlier, they also finish earlier, at 2:25, middle schools at 3:10 and senior high schools at 3:55.  All school districts establish their own times and means of transportation within guidelines set by their own state.