Most public school districts don’t have much control over the numbers of students that come through their doors. Once the boundaries of a district and its schools are established, public schools generally are required to accommodate everyone of age within those borders that seeks admission.

So it’s no surprise that the largest U.S. school district can be found in the largest U.S. city. New York City easily tops this year’s AS&U 100 list of the largest public school systems, with 1,041,437 students in 2011-12. The enrollment numbers were compiled from state education departments or individual districts.

[View the 2014 AS&U 100 here.]

But school districts aren’t required to and don’t often follow municipal borders. Districts can encompass an entire county (or, in the case of Hawaii, the whole state), or they can split a city into several separate systems. School systems can be made up of only elementary schools, only high schools, or can be responsible for all grade levels in a unified district.

So although California has twice as many people as Florida (38 million compared with 19 million, according to 2012 U.S. census estimates), California has only two school systems with more than 100,000 students, compared with seven in Florida. That’s because Florida, one of many states that has countywide districts, has only 67 school systems. California has 15 times as many districts as Florida—540 elementary, 80 high school, 338 unified and 80 other kinds of districts.

The numbers also become harder to track as charter schools become more prevalent. Although charter schools are considered public schools, their enrollment numbers may or may not be included in the school district where they are found. Much of the enrollment drop in the Washington, D.C., school district can be attributed to an increase in charter school numbers, which are not included as part of the school system’s total. In 2001-02, Washington was one of the 50 largest districts with more than 68,000 students. By 2011-12, it had fallen out of the top 100 and had about 45,000 students. Over that same decade, charter school enrollment in the District of Columbia climbed from 10,679 to 31,562.

Reform efforts that place some failing schools under the control of state-run systems have caused districts such as Detroit and Orleans Parish to experience severe enrollment drops. 

As is the case every year, the changes in the list from year to year are minimal. For 2011-12, 99 of the 100 largest school systems are the same as those in 2010-11. The only change is at No. 100; the Shelby County (Tenn.) district is supplanted on the list by San Juan (Calif.) district.

A look at 25-year enrollment trends provides more vivid evidence of change. Student numbers in the Loudoun County (Va.) district, part of the Washington, D.C., area, have nearly quintupled from 1986 to 2011, and it now is the 57th-largest district. The Douglas County (Colo.) district south of Denver is more than six times larger than it was in 1986 and is now the nation’s 63rd-largest school system.

The largest declines over 25 years are in big cities. The Baltimore City district’s numbers are 24 percent lower in 2011 compared with 1986; Atlanta’s numbers also declined 24 percent in that time.

View the 2013 AS&U 100 charts:

Elementary and Secondary

Higher Education Institutions

To see the charts as they appear in the September 2013 issue, visit the digital edition and click on AS&U 100.