Pre-kindergarten classes for students in New Jersey's poorest districts are proving beneficial well into the fourth and fifth grades. And the benefits may not be just in academic performance, but in lower school costs later on.

A seven-year study released last week followed 700 students who had been enrolled in pre-K in the state's 31 so-called Abbott districts. In Abbott v. Burke, the New Jersey Supreme Court required the state to provide high-quality pre-kindergarten classes for students in these low-income districts. The first classes of 3- and 4-year-olds began in 1999.

In later rulings the court specified that the the two-year program, which is now among the most rigorous in the nation, must utilize certified teachers, research-based curriculum and limit class sizes to 15 students. Classes are provided by a mix of public and private schools.

This doesn't come cheap. Next year, the cost of the program is expected to reach $648 million to serve 45,000 children.

Which is why the findings in the latest study by the National Institute for Early Education Research at Rutgers University are so encouraging. The study found that, on average, students who had access to pre-K were three-quarters of an academic year ahead of similar students in the fourth and fifth grades.

Students who had been through the pre-K program scored better in language arts, math and science tests. And that difference was more pronounced in the New Jersey study than in similar studies examining the results of pre-K in other states. The benefit was also greater for students who had attended two years of pre-kindergarten, as opposed to one.

What's more, these former pre-K students also were less likely than other students to have been held back a grade or to have been identified as requiring special education classes. By not needing special classes or repeating grades, they are saving their school districts money.

The education value of pre-K education is well-established. Other studies have shown that the leg up it gives students extends to success in later grades, increased college acceptance and even better jobs.

In 2009, a plan to extend pre-K to every school district in New Jersey was cut from the budget when it became clear that the state simply couldn't afford it. Unfortunately, that situation hasn't changed. While some districts have created their own pre-K programs, education advocates continue to call for universal pre-K.

Certainly this study bolsters that argument, and offers hope that if we invest in giving students a solid beginning, we might see savings down the line.