How much more evidence do we need? The case for all-day kindergarten is too strong to ignore.

• Author: Feldman, Sandra
• Position: The AFT on Critical Issues in Public Education

To inner-city elementary school teachers, it's as plain as the nose on your face: High-quality, all-day kindergarten gives at-risk children a better chance to succeed in school. That's because poor kids often enter school without knowing their numbers or letters--or even how to hold a crayon. Yet too many states have ignored the evidence and failed to provide all children with the opportunity to attend all-day kindergarten.

There's now a substantial body of research confirming what many teachers and parents have long recognized. For example, in Philadelphia, a recent study found that all-day kindergarten helps children from low-income families perform better. And it saves the school district millions of dollars because it reduces the number of students who have to repeat a year.

Research in Minneapolis shows that minority children in all-day kindergarten gained literacy skills much faster than their peers in half-day programs, helping to close the achievement gap.

These findings are reinforced by an impressive new study from Montgomery County, Maryland. At-risk students in the county's all-day kindergarten programs made significantly greater progress in language proficiency than...