Upper Marlboro, Md. ? Scores of grumbling parents facing a threat of jail lined up at a courthouse Saturday to either prove that their school-age kids already had their required vaccinations or see that the youngsters submitted to the needle.

The get-tough policy in the Washington suburbs of Prince George’s County was one of the strongest efforts made by any U.S. school system to ensure its youngsters receive their required immunizations.

Two months into the school year, school officials realized that more than 2,000 students in the county still didn’t have the vaccinations they were supposed to have before attending class.

So Circuit Court Judge C. Philip Nichols ordered parents in a letter to appear at the courthouse Saturday and either get their children vaccinated on the spot or risk up to 10 days in jail. They could also provide proof of vaccination or an explanation why their kids didn’t have them.

By about 8:30 a.m., the line of parents stretched outside the courthouse in the county on the east side of Washington.

Many of them complained that their children already were properly immunized but the school system had misplaced the records. They said efforts to get the paperwork straightened out had been futile.

School officials deemed the court action a success. School system spokesman John White said the number of children lacking vaccinations dropped from 2,300 at the time the judge sent the letter to about 1,100 Friday.

After Saturday’s session, 172 more students were brought into compliance, including 101 students who received vaccinations at the courthouse and 71 whose records were updated.

That still left more than 900 students out of compliance with vaccination requirements, White said.