Until the 1980s, the American homeless population comprised mainly older males. Today, homelessness strikes much younger part of society. In fact, a 25-city survey by the U. S. Conference of Mayors in 1987 found that families with children make up the fastest growing part of the homeless population. Many homeless children gather in inner cities; this transient (变化无常的) and frequently frightened student population creates additional problems — both legal and educational — for already overburdened school administrators and teachers.
Estimates of the number of homeless Americans range from 350,000 to three million. Likewise, estimates of the number of homeless school children vary radically. A U. S. Department of Education report, based on state estimates, states that there are 220,000 homeless school-age children, about a third of whom do not attend school on a regular basis, But the National Coalition for the Homeless estimates that there are at least two times as many homeless children, and that less than half of them attend school regularly.
One part of the homeless population that is particularly difficult to count consists of the "throwaway" youths who have been cast of their homes. The Elementary School Center in New York City estimates that there are 1.5 million of them, many of whom are not counted as children because they do not stay in family shelters and tend to live by themselves on the streets.
Federal law, the Stewart B. McKinney Homeless Assistance Act of 1987, includes a section that addresses the educational needs of homeless children. The educational provisions of the McKinney Act are based on the belief that all homeless children have the right to a free, appropriate education.
It is implied in the first paragraph that ______.