Presidents at least as far back as Bill Clinton have made attendance a priority of their school-reform efforts, in part because of the social costs of youngsters not attending. There's a direct line from truancy to juvenile crime, gang membership, and drug use, according to the U.S. Department of Justice. There's an equally direct line from truancy to dropping out of school, and from there to increased incidences of teen pregnancy, poor health, and dependency on welfare. States and school districts vary in how they define truancy, which means that nationwide truancy statistics don't exist. In Maryland, a truant is someone who has 18 unexcused absences per semester. In Texas, it's 10 unexcused absences within six months. In Florida, it's 15 in 90 calendar days. Complicating any attempt to compare statistics are divergent state compulsory-education laws. In D.C., youngsters must attend school until age 18, in Maryland until age 16, and in Pennsylvania until 17. In this article, the author discusses the challenges of keeping kids in school.