UPPER MARLBORO, Md. —  Hundreds 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. [script removed] /**/ [script removed]

"It was very intimidating," Territa Wooden of Largo said of the letter. She said she presented the paperwork at the courthouse Saturday and resolved the matter.

"I could be home asleep. My son had his shots," said Veinell Dickens of Upper Marlboro, who also blamed errant paperwork.

Aloma Martin of Fort Washington brought her children, Delontay and Taron, in 10th and 6th grade, for their hepatitis shots. She said she had been trying to get the vaccinations for more than a month, since the school system sent a warning letter. She had an appointment for Monday, but came to the courthouse to be safe.

"It was very heavy handed," she said of the county's action. "From that letter, it sounded like they were going to start putting us in jail."

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. Hundreds more were expected to be in compliance after Saturday's session.

Officials said they did not know how many students got shots Saturday and how many merely had paperwork problems. It was also unclear how many claimed medical or religious exemptions to the requirement.

White said the school system, with about 132,000 students, has been trying for two years to get parents to comply with state law. That law allows children to skip vaccines if they have a medical or religious exemption.

Maryland, like all states, requires children to be immunized against several childhood illnesses including polio, mumps and measles. In recent years, it also has required that students up to high school age be vaccinated against hepatitis B and chicken pox.

Nichols said nobody actually came before him Saturday, but he was there if any parent asked to see him.

The judge noted the unhappy looks of some of the kids in line waiting for vaccinations.

"It's cute. It looks like their parents are dragging them to church," Nichols said.

Any children who still lack immunizations could be expelled. Their parents could then be brought up on truancy charges, which can result in a 10-day jail sentence for a first offense and 30 days for a second.

Prince George's State's Attorney Glenn Ivey couldn't say Saturday whether he would prosecute parents who fail to comply.

"We have to sit down with school and health services," he said. "We haven't ruled anything out. We need to figure out where we stand."

Several organizations opposed to mass vaccinations demonstrated outside the courthouse. While the medical consensus is that vaccines are safe and effective, some people blame immunizations for a rise in autism and other medical problems.

"People should have a choice" in getting their children immunized, said Charles Frohman, representing a physicians' group opposed to vaccines.