A high school diploma just ain’t what it used to be.

In today’s knowledge economy, people who don’t get educated beyond high school generally do more poorly than college graduates in achieving some of life’s most basic goals — getting and keeping a good job, earning high wages, having career flexibility and the freedom to thrive in a bigger world.

This achievement gap will only widen. Many educators and policy experts agree that post-secondary education no longer can be considered optional. Every high school student, whether interested in European literature or car engine repair, needs to go to college.

In Hawaii’s public high schools, progress has been made to encourage motivated students to think bigger. The University of Hawaii and the state Department of Education have teamed up to offer dual-credit and Early College programs that allow public school students to earn college credit while in high school.

Now UH has a plan to reach more Hawaii students, especially those who might not consider college, by removing one big barrier — the cost.

Legislation proposed by UH would create the Hawaii Promise program, which would cover the direct costs of attending one of UH’s seven community colleges, costs that include tuition, books, fees, supplies and transportation.

It’s an intriguing idea that has been implemented in other states and promoted nationally by then-President Barack Obama, who wanted community college to become “as free and universal in America as high school is today.”

Making the transition from high school to community college as seamless as possible makes sense. Community colleges offer associate degrees and certificate programs that traditional four-year colleges may not, making it easier for students to continue their education in a field they’re interested in.

With Hawaii Promise, a student’s need would be determined through the federal Free Application for Federal Student Aid (FAFSA). The state would cover whatever costs remain unmet after scholarships and federal and state grants are factored in.

For those who really need a leg up, Hawaii Promise can be their golden ticket to a larger world.

There’s no specific GPA requirement. Students would not be required to get a student loan to cover costs. They must be eligible for resident tuition and enrolled in a degree or certificate program at a community college for six or more credits per semester.

UH officials estimate that more than 1,000 students could benefit; the estimated cost to the state would be a modest $2.5 million.

If the program proves popular, those costs can be expected to rise. But that would be a healthy thing.

The percentage of Hawaii high school students attending college is gradually increasing, but it could be higher. The public schools’ Class of 2015 sent 56 percent of its graduates to college, higher than in years past but no better than the previous year, according to a recent College and Career Readiness Indicators report.

Generally, the numbers are lower for at-risk students — Native Hawaiians and Pacific Islanders, and those who are poor. They could benefit the most by going to college.

A study last year by the state Department of Business, Economic Development and Tourism found that someone with an associate’s degree earned nearly $6,000 more a year than someone with just a high school diploma. Likewise, poverty rates were lower for those with an associate’s degree — 8.7 percent versus 12 percent for high school graduates.

Lawmakers are considering expanding Hawaii Promise to include all 10 of UH’s campuses, including its three four-year universities. UH officials like the idea, and estimate it would cost about $13.5 million initially and increase with time.

But the additional money might be too heavy a lift this year.

Given gloomy tax revenue forecasts and a skeptical Legislature, a bigger program might be too much, for now.

For community colleges, though, the investment is a sound one.