There was a 74 percent increase in the number of home-school children between 1999 and 2007.

Gail Mulligan of the Department of Education's National Center for Education Statistics said a variety of reasons led to 1.5 million children being primarily educated in U.S. homes in 2007, USA Today said Monday.

Among the home-schooling reasons given by parents in a 2007 survey were moral and religious factors, along with concerns about family time and finances.

Whatever the cause for the increase in the number of home-schooled students, Mulligan said, the figures will likely keep rising.

"There's no reason to believe it would not keep going up," she told USA Today.

Robert Kunzman, an Indiana University associate professor, agreed, saying the home-schooling movement has steadily expanded beyond conservative Christian groups.

Officials say an increasing amount of U.S. parents are embracing home-schooling to allow their children to learn at their own pace.