In theory, improving low-income families' housing and neighborhoods could also improve their children's health, through any number of mechanisms. For example, less exposure to environmental toxins could prevent diseases such as asthma; a safer, less violent neighborhood could improve health by reducing the chances of injury and death, and by easing the burden of stress; and a more walkable neighborhood with better playgrounds could encourage children to exercise, making them less likely to become obese. Yet although neighborhood improvement policies generally achieve their immediate goals- investments in playgrounds create playgrounds, for example-Ingrid Gould Ellen and Sherry Glied find that many of these policies don't show a strong effect on poor children's health. One problem is that neighborhood improvements may price low-income families out of the very neighborhoods that have been improved, as new amenities draw more affluent families, causing rents and home prices to rise. Policy makers, say Ellen and Glied, should carefully consider how neighborhood improvements may affect affordability, a calculus that is likely to favor policies with clear and substantial benefits for low-income children, such as those that reduce neighborhood violence. Housing subsidies can help families either cope with rising costs or move to more affluent neighborhoods. Unfortunately, demonstration programs that help families move to better neighborhoods have had only limited effects on children's health, possibly because such transitions can be stressful. And because subsidies go to relatively few low-income families, the presence of subsidies may itself drive up housing costs, placing an extra burden on the majority of families that don't receive them. Ellen and Glied suggest that policy makers consider whether granting smaller subsidies to more families would be a more effective way to use these funds.