Promising first-year results from a study of full-day preschool in a high-poverty suburban Denver school district have stoked optimism about a new financing approach officials are testing there.

It’s called Pay For Success and has gained traction nationwide in recent years as a way to pay for social programs that yield long-term dividends but are expensive to launch.

The struggling 9,600-student Westminster Public Schools is using a version of the complicated financing model, also known as social impact bonds, to fund and rigorously evaluate full-day preschool.

While similar projects in Salt Lake City and Chicago have been underway longer, Westminster’s three-year pilot project provides the first Colorado case study of Pay For Success as a preschool expansion tool.

It’s also a key component of the early childhood efforts outlined in the district’s state-mandated improvement plan. Only about a third of Westminster kindergartners meet expected benchmarks when they start school.

This year, about a quarter of the district’s 600 preschoolers attend full-day programming — at a cost of about $10,000 per student.

The full-day classrooms are the most expensive in the district because of state class size and student-teacher ratio requirements, but not as pricey as some high-quality preschool programs elsewhere.

The idea behind Pay For Success financing is that private investors or philanthropists pay upfront for social programs and get repaid with interest if those programs save public money by preventing the need for costly services such as special education or reading remediation. If a project doesn’t yield the hoped-for savings, the investors lose some or all of their money.

Westminster Public Schools dipped its toes into Pay For Success waters last year, offering full-day preschool to 112 4-year-olds at seven elementary schools. Two foundations — Gary Community Investments and the Ben and Lucy Ana Walton Fund of the Walton Family Foundation — put up a combined half million dollars for the project.

(The Walton Family Foundation and Gary Community Investments — through the Piton Foundation — are Chalkbeat funders).

Westminster’s pilot is not a full-fledged Pay For Success transaction because the state is not a partner in the agreement as would typically be the case. In addition, the project agreement doesn’t require the two funders to be repaid fully if the district’s full-day preschool program yields the hoped-for savings.

However, the gold standard study by outside evaluators comparing full-day and half-day preschoolers is standard Pay For Success fare. It’s also a key part of what funders and other school districts may be looking at as they consider preschool expansion efforts.

So far, Westminster’s results look good.

Full-day preschoolers there performed better than their half-day peers on a bevy of early childhood assessments that measure everything from early literacy to social and emotional development.

“We’re seeing some real statistical significance in terms of full-day (preschool),” said Mat Aubuchon, the district’s director of early childhood education.

Further evaluations over the next two years will provide more definitive results, he said.

In addition to preliminary data gleaned from the official evaluation, Aubuchon said the district has discovered some unanticipated benefits of the full-day program. These include higher attendance rates in full-day preschool classrooms and increased likelihood that full-day preschoolers will come back for kindergarten.

While 60 percent of half-day preschoolers returned for kindergarten this year, that number was 76 percent for full-day preschoolers.

Asked if the district’s full-day preschool initiative might continue beyond year three as a full-blown Pay For Success project, Aubuchon said, “I certainly hope so.”

Steffanie Clothier, investment director for child development at Gary Community Investments, said Westminster’s project will provide a valuable evidence base for other districts interested in preschool expansion even if they don’t use Pay For Success.

“I think Pay For Success is a great way to help understand the financing and short term and longer term savings from preschool programs,” she said. “But I don’t think it’s essential as a funding stream.”