Monday, September 8 marked the start of an expanded pre-K program implemented by Mayor Bill de Blasio in New York City. The program, which provides free full-day classes to thousands of four year olds at the city’s public schools, is part of a growing movement in the U.S. toward universal preschool as a means of combating economic and social inequality. In addition to de Blasio, advocates of expanded pre-K access include President Barack Obama and Secretary of Education Arne Duncan, who recently called high-quality preschool “a sure path to the middle class.”

While studies have shown that high-quality preschool indeed has positive effects on low-income children in terms of later educational attainment, some scholars and journalists have voiced reservations about the ability of pre-K programs to diminish inequality. Journalist Sarah Jaffe has noted that with de Blasio’s program in particular, lack of adequate funding for the program may inadvertently create a “patchwork” system that perpetuates other economic inequalities, like low salaries for the preschool teachers, who are overwhelmingly women.

Karl Alexander, co-author of the RSF publication The Long Shadow, further points out in a new op-ed for Quartz, “The reality is that there is no guarantee low-income children will succeed academically simply because they have a good preschool experience.” He continues, “To fully reap the benefits of early childhood education, these students need continued support outside the classroom through strong summer programs and after-school care.”

Drawing from the 25-year study of Baltimore schoolchildren detailed in The Long Shadow, Alexander explains the predicament of what he calls “summer slide,” or the tendency for low-income children who have kept up academically with their affluent peers during the school year to fall behind during the summer months, when fewer resources and educational experiences are available to them. He further notes that a strong preschool education won’t erase the forces of poverty that many children confront daily in their homes and neighborhoods. Alexander concludes, “While universal access to preschool is essential, we must remember there is no silver bullet.”

Click here to read Alexander’s op-ed in full on Quartz.

Click here to read more about The Long Shadow or purchase a copy of the book.