What's a fair way to measure a teacher's worth? That's the biggest problem with implementing a merit pay system for teachers. It's not the why — we all want to reward teachers who do a great job — but the how.

So it's intriguing to see Kamehameha Schools tackle the issue, with a high-profile experiment called Ka Pi'ina. As described by Advertiser reporter Loren Moreno on Monday, Ka Pi'ina would establish a program that would buck the traditional seniority-based pay scale in favor of one that rewards professional ambition and performance. The goal: helping students learn more by helping their teachers become better educators.

There are good reasons to hope for Ka Pi'ina's success.

Giving younger, energetic teachers a reason to stick with the profession — and not abandon it for more lucrative pastures — can help raise student performance and ease chronic teacher shortages.

It could also raise the quality of teachers overall; financial incentives would encourage more teachers to seek professional enrichment and make additional efforts to raise student performance. And those dedicated teachers who do it well now — quietly, without compensation — certainly deserve more.

Now more than ever, the need is there. In this competitive global economy, students need a quality education that takes them beyond a basic high school diploma. It will take more and better-qualified teachers at all levels to meet this demand.

Of course, the devil is in the details. Teachers unions, including the Hawai'i State Teachers Association, question whether any merit-pay system can be applied equitably.

"We can't simply base a merit pay system on student performance or test scores," says HSTA president Roger Takabayashi. Fair enough. Unlike private schools, public school teachers must work with students of all levels of ability.

But the bottom line must be improving the quality of a student's education. Merit pay offers a way to do that. Developing a smart system for Hawai'i's public school teachers must be a top priority for the HSTA and the state.