Education officials in the District announced yesterday that they would begin referring the cases of 434 students who lack proof of immunization to the city's Family Court, where the children's parents and guardians could be fined or jailed and ultimately charged with child neglect.

All of the children have been barred from attending classes, which began Sept. 1.

Officials said the referrals to the judicial system are a drastic but unavoidable option because numerous outreach efforts have failed to compel parents and guardians to obtain or document the required shots. A 1979 city law prohibits students from attending school without current immunization records. A major push to enforce the law began in 2002.

Of the 434 children, 379 are in middle, junior high or senior high schools. Although many of them had been immunized in previous years, their records are missing or they have not received catch-up shots or booster doses against such diseases as tetanus, diphtheria, chickenpox and hepatitis B, officials said.

Ralph H. Neal, the assistant superintendent who oversees enforcement of the immunization rules, said that numerous notices have been mailed since the spring to remind parents of the requirements. City workers have knocked on doors and placed telephone calls to get families to respond.

"Principals have made phone calls and even taken kids to the clinics themselves," Neal said. "It is definitely the parents' responsibility to make sure that the students are in compliance with the immunization law. The court system will have to fulfill its responsibility with respect to charging families with truancy or neglect."

Under a 1990 law, parents who fail to make sure that their children attend school can be fined as much as $100 and jailed for as many as five days for each offense. The Family Court, a division of D.C. Superior Court, has assigned a judge to focus on truancy cases.

The District appears to have an especially severe problem with immunizations. In Loudoun County, for example, very few students showed up to school on the first day without immunizations, and those who did received their shots within days, said Wayde B. Byard, a spokesman for the school system. In Fairfax County, letters and phone calls are nearly always sufficient to get parents to comply quickly, said Diana F. Jarrett, coordinator of student registration services for the county school system.

Lost records and missing immunizations are common in low-income urban school districts, where many families lack consistent access to preventive health care, said Deborah L. Wexler, an advocate for childhood immunizations.

"People move frequently, from place to place and clinic to clinic, and there's the issue of lost or unretrievable records," said Wexler, a family physician who heads the Immunization Action Coalition, based in St. Paul, Minn., which tries to increase vaccination rates. "Kids fall behind in their vaccinations. They slip through the cracks. A lot of families live from day to day, and immunization just isn't a top priority when there are other crises going on."

Most immunizations occur in infancy or early childhood. However, children are supposed to receive a tetanus-diphtheria booster dose about age 11, and children who have not received a second dose of immunization against mumps, measles and rubella before kindergarten generally receive it when they enter middle school. The hepatitis B vaccine was not recommended until 1991, and vaccinations against chickenpox began in 1995, so older children might lack those immunizations.

Karyn L. Berry, interim deputy director for primary care and prevention at the D.C. Department of Health, said that lost records have become less of a problem since the department began a computerized immunization registry.

The health department is urging parents to first contact their primary-care physicians to arrange for immunizations, but has arranged for six clinics to provide free shots for families lacking other options. For information about the clinic locations, call 800-MOM-BABY (800-666-2229).

Staff writers Maria Glod and Rosalind S. Helderman contributed to this report.