An article looks at the research on preschool and its benefits. (Paul Efird/AP)

“Preschool has never been more popular,” Kirsten Weir writes in the May issue of Monitor on Psychology, pointing to President Obama’s Preschool for All initiative and New York Mayor Bill de Blasio’s efforts to expand preschool access in the city.

“But in many ways, the national conversation about early education is just getting started,” she notes. “The top question about universal pre-K — whether it is worth the cost to taxpayers — remains up for debate. That’s partly because studies of early education have found mixed results.”

Two long-term studies have been most influential: The Abecedarian Project in 1970s North Carolina and the Perry Project, which followed 1962 preschoolers in Michigan for several decades.

But these studies were intensive and expensive, making them difficult to update and to use as models in an era of lean education budgets, Weir says. Today, she points out, researchers are trying to build on what we already know. For example, she cites a 2013 meta-analysis of 84 studies of preschool programs conducted from 1965 to 2007: It concluded that early education produced gains in language, reading and math skills that was equal to about a third of a year of extra learning.

Other studies, she notes, have raised concerns about return on investment of such programs. For example, a report released in December by the Department of Health and Human Services concluded that third-graders who had been in Head Start before kindergarten showed “no clear benefits in cognitive or social-emotional development.”

There’s a lot here to think about. The full article, with links to the research, is available at the magazine’s Web site,