In America's classrooms, unfortunately, family income can be an indicator of the quality of a student's teachers.

Despite federal rules that require highly qualified teachers in every class, poor students are still more likely to be taught by inexperienced or unqualified teachers or those teaching outside of their areas of expertise, according to a recent study by Education Trust. Because good instruction is directly tied to student achievement, too many poor children are at a disadvantage.

To change that inequity, states, school districts and education programs must step up efforts to improve teacher training and restructure school staffing to expand strong instruction to more students.

Ten years ago, federal lawmakers acknowledged the problem and included teacher-quality provisions in the No Child Left Behind law. Those rules required states to ensure that teachers were "highly qualified" by 2006 and specifically included in-field assignment among the criteria.

State data given to the U.S. Department of Education reported good progress for 2007-08, with 95 percent of secondary-level core academic classes having good teachers. But the staffing data that teachers themselves reported during same period told a different story.

That survey reported an actual out-of-field rate three times as high as the state-reported rates. According to those actually doing the teaching, about 15 percent of secondary core academic classes are taught by educators with neither certification nor an academic major in that subject area. In high-poverty secondary schools, students were still almost twice as likely to be taught by a first-year or out-of-field teacher as were their more-affluent peers.

The problem is not limited to big cities. Concentrations of lower-income students in suburbs, small towns and rural areas are also taught more often by inexperienced teachers.

Compared with the national figures, Minnesota does a better job. About 9 percent of core academic secondary courses were taught by less-qualified teachers, compared with 20 percent or more in about a dozen other states. But Minnesota also has one of the largest learning disparities between white students and a growing population of lower-income students of color -- some of whom are also immigrant English-language learners.

To address the problem, Education Trust wisely points out that federal law says that low-income and minority students should not be taught disproportionately by unqualified teachers. The organization recommends that states adopt similar rules so that state leaders can keep districts from striking contract agreements that interfere with fair access to good teachers. The think tank also suggests using state authority to intervene in low-performing schools, providing incentives to teach in high-poverty schools and holding teacher-preparation programs accountable for producing effective educators.

A number of efforts are underway in Minnesota to achieve those goals. The state board of teaching recently announced that aspiring teachers will be given a more rigorous test with higher standards tied to the state's K-12 standards. Some districts have negotiated more flexible staffing rules in their teacher contracts.

And the Bush Foundation is spending $10 million to help colleges and universities improve teacher preparation and support new teachers during their first assignments. Those types of initiatives can move school systems closer to providing quality instruction for all kids -- regardless of family income.