Nearly 40 million Americans are locked into dead-end jobs because they do not have a high school diploma. A daylong exam called the General Educational Development test, or G.E.D., provides the equivalent of a high school diploma — and better chances in the job market — to those who pass it. Nearly 800,000 people take the exam each year, and about 500,000 pass.

But here is the stunning — and sad — truth about this exam: Success depends heavily on where you live. In Iowa, Kansas and Delaware, 90 percent or more of those who take the test pass. In Alabama, Mississippi, New York and the District of Columbia, less than 60 percent pass.

What accounts for the difference? Preparation. States with low success rates do a poor job of prepping students for the exam. The reverse is true in states with high scores. In Iowa, for example, students take a diagnostic pretest, then receive instruction in their weak areas, then take a practice test. In 2009, 98 percent of those who took the test in Iowa passed the G.E.D. exam.

The test is free in some states and costs as much as $400 in others. Either way, states should make sure people have a legitimate shot at success.

A G.E.D. program developed by New York City's Department of Education may help show New York State — and other states with poor test results — the way forward. The program uses innovative instructional techniques to make sure students are fully prepared.

Over the last several years, the program has a pass rate of about 78 percent, more than 20 percentage points higher than the statewide rate.

The city's program has so impressed the American Council on Education, the nonprofit group that owns the G.E.D., that it will soon begin a pilot program in District 79, which deals with alternative schools and programs. Underwritten by a $3 million grant from the MetLife Foundation, this pilot program is intended to develop a model for educating more adults more quickly so they can pass the G.E.D. and move on with their careers.

These improvements are timely because the G.E.D. test itself is about to get tougher. The new test, to be developed over the next several years, is being revised to conform to more rigorous educational standards proposed earlier this year by the National Governors Association and state school superintendents.

These standards set forth ambitious new goals for what children should learn from kindergarten through high school and have already been embraced by most states. Among other things, they would require students to develop reasoning skills earlier in their educational experience and set higher, college-level standards in math, English and science.

For all these reasons, states — including New York — will need to invest much more heavily in programs that prepare people for the G.E.D. At stake is their economic future — and the country's.