Student are supposed to get vaccinated against certain diseases. But what if the parents don't take care of it? Make it costly for them not to, like sending them to jail. Here is the intro to one of the articles:
"UPPER MARLBORO, MD. — The threat of jail time injected a little motivation into scores of parents who lined up around the courthouse Saturday to get their children vaccinated on the spot or prove they've already had the shots.
It was one of the strongest efforts yet by a U.S. school system to ensure that youngsters are immunized, upsetting some parents who grumbled that Prince George's County officials went too far and irking opponents of mass vaccinations, who demonstrated outside.
Two months into the school year, county officials realized more than 2,000 students didn't have the vaccinations required to attend class. So Circuit Court Judge C. Philip Nichols ordered parents in a letter to appear at the courthouse Saturday or risk 10 days in jail."
You can read about it here and here and here