Summer vacation is one of the predominant causes of the achievement gap in America's schools. While middle- and higher-income children spend their summers engaged in activities and enrolled in programs that strengthen and reinforce learning, the vast majority of children in low-income communities have little or no access to such opportunities. By the time school begins each year, low-income children's lack of access to enriching summer activities results in their falling weeks, if not months, behind their more advantaged peers. This Information Capsule summarizes research indicating that low-income students experience greater learning loss over the summer months than their higher-income peers because they are less likely to participate in summer enrichment activities. This report also reviews the characteristics of effective summer learning programs and provides a brief summary of research suggesting that participation in these programs helps students maintain or even increase their academic skills over the summer months, especially in reading. Finally, research conducted on summer book reading programs is discussed. Studies suggest that providing books to low-income children and encouraging them to read is a cost-effective and replicable approach that can help to develop their reading skills over the summer. (Contains 1 table.)