More than a half-million children are in foster care. By definition, they've had it tough.

Social service agencies hesitate to remove children from their natural homes absent unmistakable signs of truly serious problems, such as neglect or abuse.

Child-welfare professionals recognize that, even when they extricate children from deeply troubled home situations and place them in protective, supportive foster homes, the change takes a toll on the children. It tears the little ones away from all that is familiar - neighborhoods, friends and entire social networks - at a critical time in their development.

Often, such gut-wrenching changes keep coming. Once in the system, children typically face one or two changes in placement each year. Nearly one in five foster children remains in care for three years or more. Such disruption increases the probability of later social problems.

Typically, a change of address also forces foster children to change schools. That alone can jeopardize their future. Studies show that children who experience frequent disruptions in their education are more likely to perform below grade level.

A recent survey of education research conducted for the Pew Charitable Trusts confirms that poor performance in school makes it harder to climb the economic ladder in later life. So the education disruption common in foster care can lead to lasting economic as well as social problems for these children.

To deal with the problem, some education experts advocate using vouchers to enable foster children to stay in the same schools even when their home placements change.

Under this approach, a foster child would be able to stay enrolled at his or her current public school, even if the new foster home is located outside the school's service boundaries. The voucher payments would go to the school teaching the child.

Vouchers also could be used to help children attending private schools before entering foster care to continue in those familiar classrooms.

Granted, education vouchers have been highly controversial when proposed as a general remedy for underperforming schools. But the political polarization frequently triggered by these broad proposals has been muted considerably when this far narrower application of vouchers has been suggested.

One of the first groups to broach the idea of using vouchers to ease education disruptions for foster children was the Maryland Public Policy Institute. That outfit articulated the idea in a 2005 paper authored by a Heritage Foundation colleague, Dan Lips.

The following year, the Institute held focus groups to gauge public attitudes in the state. It found strong support for using vouchers to help foster children remain in the same school.

Soon thereafter, the Goldwater Institute in Arizona analyzed how the idea might be used in concert with that state's foster care program. The Institute's findings inspired a state lawmaker to propose a voucher program for foster children. In 2006, the measure passed Arizona's Republican-controlled Legislature and was signed into law by Gov. Janet Napolitano, a Democrat.

Since then, formal legislation to voucherize education for foster children has been introduced in several other states, including Florida, Maryland, Tennessee and Texas.

To be sure, vouchers are no panacea for the problem of education disruption. Some foster care placements will be so far away from the child's original school that the travel time would make continued enrollment difficult or impossible. And in some jurisdictions, vouchers may be unnecessary to assure continuity.

In the District of Columbia, for example, "out of boundary" children can often continue in the same public school even if they change addresses. But for vast numbers of foster children, vouchers could prove to be key to doing well in school.

The need to improve educational stability for foster children is being recognized on Capitol Hill, too. Congress recently passed legislation requiring states to help ensure that when placed in a new home, foster children remain in the same school whenever possible.

The body of research into how school disruption adversely affects children - and their educational performance - has grown greatly. As a result, social scientists are giving greater priority to finding ways to help foster children continue in familiar schools.

Politicians and educators alike should recognize the unique challenges facing these at-risk children and support policies that can help give them a real chance to succeed.

Education vouchers can do that, by fostering steady, vitally important school relationships - with teachers, classmates and educational programs - in young lives yearning for stability.

Stuart Butler is vice president for domestic-policy issues for the Heritage Foundation (www.heritage.org).