Large numbers of low-income children who begin formal schooling with many disadvantages - poor medical care, homelessness, an uneducated mother, for example - not only struggle with schoolwork but hurt the achievement of other children in their classrooms, according to a new study.

A team of researchers from the University of Pennsylvania studied more than 10,000 children who were enrolled in public schools in Philadelphia from kindergarten through third grade. They found that in schools with a high concentration of children with “risk factors,” the academic performance of all children - not just those with disadvantages - was negatively affected.

For example, researchers found that children who were homeless or mistreated disrupted their classrooms, pulling down reading achievement and attendance rates among children who were not homeless or mistreated. Along the same lines, schools filled with many students who did not receive adequate prenatal care had overall poor reading achievement, even among those children who did get prenatal care.

Led by John Fantuzzo, the peer-reviewed study was published last week in Educational Researcher.

The researchers created a sophisticated data system that combined information not just from the Philadelphia public schools but from a range of social service agencies and other public sources, to examine the risks and factors that affected thousands of children, even dating back to before they were born.

Fantuzzo’s research suggests that the national movement that holds schools accountable by tracking the academic performance of children by subgroups - defined by race, income, disability and whether English is a first language - may be too blunt and doesn’t recognize that “at risk” students can affect their peers. A better approach to accountability would be to target support and interventions to certain “at risk” children, so that the entire school could benefit, the researchers said.