Is preschool worth it? Policymakers, parents, researchers and us, at NPR Ed, have spent a lot of time thinking about this question.

We know that most pre-kindergarten programs do a good job of improving ' specific skills like phonics and counting, as well as broader social and emotional behaviors, by the time students enter kindergarten. Just this week, a study looking at more than 20,000 students in a state-funded preschool program in Virginia found that kids made large improvements in their alphabet recognition skills.

So the next big question to follow is, of course, Do these benefits last?

New research out of North Carolina says yes, they do. The study found that early childhood programs in that state resulted in higher test scores, a lower chance of being held back in a grade, and a fewer number of children with special education placements. Those gains lasted up through the fifth grade.

The research, published this week in the journal Child Development, studied nearly 1 million North Carolina students who attended state-funded early childhood programs between 1995 and 2010, and followed them through fifth grade.

They concluded that the benefits from these programs grew or held steady over those five years. And when the researchers broke the students down into subgroups by race and income — they found that all of those groups showed gains that held over time.

"Pre-kindergarten and early education programs are incredibly important," says Kenneth Dodge, the lead author on the study and the director of the Duke Center for Child and Family Policy. "Especially for parents, for business leaders — because of the workforce development aspect — and for policy makers who are spending the money on it."

This new research confirms what researchers recently found in Tulsa, Okla. – one of the most highly regarded preschool programs in the country. In that study, children who attended Head Start had higher test scores on state math tests up through eighth grade.

Eearlier studies have found the positive effects fade as students move into elementary school — this large study from Vanderbilt is one of them.

The big difference between the long-term findings in North Carolina and Tulsa and the fade out in Tennessee, researchers say, is the quality of the preschool program.

Having a high-quality program is key, says Dodge. "The long-term impact," he says, "depends entirely on quality and how well elementary schools build on the foundations set in pre-K."

North Carolina's state-funded program, known as NC Pre-K, has been praised as a model for other states.

Experts cite several key elements in "high-quality" preschool: small class sizes, student-directed learning and lots of open-ended play. And researchers have warned that outcomes are short-lived when those elements are not present.

"I think that the question is turning away from whether we should do pre-kindergarten and instead to how should we do pre-kindergarten," says Dodge.

While President Obama made universal, high-quality preschool a priority, it's unclear at this early stage whether that focus will continue in the Trump administration. Conversations about broad changes may continue to happen more at the state and local level.

Most states have some version of pre-K — 42 states plus the District of Columbia had state-funded programs in the 2014-2015 school year, according to the National Institute for Early Education Research, based at Rutgers University.

"I don't think we can anticipate that the federal government is going to roll out a single universal preschool program," says Dodge. "The reality is that preschool is becoming a state and local and community initiative."

Dodge says that's why research looking at these state programs – which often vary in size, quality and funding – is so important.

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