Maybe it's a reflection of an inevitable slowdown of the birth rate. Maybe it's because of the ailing economy. Or maybe it's because of an exodus of students to charter schools. Whatever the reason, the numbers are clear: Student enrollment among the nation's largest school districts has begun to wane.

The AS&U 100, a compilation of enrollment data and other information for the 100 school districts with the most students, shows that 21 of the 27 largest districts experienced an enrollment decline from 2006-07 to 2007-08. The 27 districts that had more than 100,000 students in 2006-07 experienced a collective decline of more than 58,000 students — from 6,102,933 to 6,044,268.

Having fewer students means less funding for school systems, most of which receive state aid on a per-student basis. If an enrollment decline becomes prolonged, administrators sooner or later will have to cope with empty or underutilized facilities. That's been the situation for several years in Detroit Public Schools, which absorbed the most severe enrollment decrease in 2007-08. It reported an enrollment of 102,494, a drop of 12.85 percent from the 117,609 reported in 2006-07. Compared with numbers from 20 years earlier, Detroit's enrollment has dropped more than 43 percent — with some 79,000 fewer students, that means a lot of empty classrooms.

Detroit school officials recently announced plans for a $500 million bond election in November that would pay for improvements to many existing facilities, but the plan also could lead to the closing of 60 schools — in addition to the many that already have been shuttered.

The Washington, D.C., school system reported the steepest one-year enrollment decline — from 56,943 in 2006-07 to 49,422 in 2007-08. Much of that drop can be attributed to a change in the way the school system reports enrollment — the 2006-07 numbers included many charter schools, but those numbers now are compiled separately from the Washington, D.C., system.

A decline in enrollment is a new phenomenon for many of these districts. Of the 100 largest districts in 2007-08, only eight reported overall enrollment declines from 1987 to 1997. In aggregate, the 100 largest districts in 2007-08 grew more than 30 percent from 1987 to 2007 — from 8,194,951 students to 10,708,738. From 1997 to 2007, 31 of the districts saw their overall enrollment drop. And from 2006-07 to 2007-08, 55 of the 100 largest districts reported fewer students.

Some districts defied the odds and continued to add students. Three of the top 100 districts experienced one-year enrollment growth of 5 percent or greater: Loudoun County, Va., (75th largest) added more than 3,600 students and grew 7.15 percent to 53,985 students. Douglas County, Colo., (81st largest) grew 5.19 percent, from 50,370 to 52,983. Katy, Texas, (76th largest) grew 5 percent, from 51,201 to 53,762. Those districts also are the ones that have had the steepest growth rate over 20 years. Douglas County has grown more than 404 percent since 1987, when it had 10,501 students. Loudoun County has grown 349 percent since its 1987 enrollment of 12,011; and Katy is 237 percent larger than 1987, when it had 15,952 students.

The school systems whose enrollment numbers have declined most precipitously over 20 years (in addition to Detroit) are Washington, D.C. (42.82 percent), Cleveland (31.06 percent), Baltimore (26.23 percent) and Atlanta (24.94 percent).

The drop in student numbers that has begun at the largest K-12 institutions is not showing up in the enrollment figures for colleges and universities. All but one of the 20 colleges with the largest enrollments gained students from fall 2006 to fall 2007, and all 20 report higher enrollments compared with fall 1997. The higher-education institution with the largest enrollment is the University of Phoenix. As an online operation not constrained by limited classroom space, it enrolled more than 224,000 students in fall 2007.

Enrollment data for 2007-08 comes from states or individual districts/institutions. Data from earlier years comes from the U.S. Department of Education's National Center for Education Statistics. Because states and local districts/institutions do not always calculate enrollment the same way federal number-crunchers do, the numbers shown here for 2007-08 may not match the NCES figures when they are released.

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