Five years ago, Congress and President Bush made a bold and historic promise. We pledged in the No Child Left Behind Act that the federal government would do all in its power to guarantee every child in America, regardless of race, economic background, language or disability, the opportunity to get a world-class education.

We have made progress toward fulfilling that commitment. Before the act was passed, most states lacked ways to track student progress and teacher effectiveness. Many state accountability requirements had no commitment to improving education for every child. Only four states had approved assessments that tracked and reported the achievement of every group of students in their schools.

Today, all 50 states have standards, assessments and accountability procedures that enable us to track the achievement of every group of students. Every school measures performance, based not on overall student population but on progress in closing achievement gaps and getting all students to meet high standards. Schools across the country are using assessments under the No Child law to identify weaknesses in instruction and areas of need for their students.

These are significant reforms, and we can't simply ignore them.

But to fulfill our promise, much more remains to be done.

The No Child Left Behind Act is up for reauthorization. Some in Congress feel the challenge is too great and want to turn back the clock on reform. One Republican proposal would even let states avoid accountability requirements and still receive federal funds.

Most of us in Congress know that a retreat to mediocrity is wrong. To meet the demands of the 21st century, we have to expand opportunity for all and keep our commitment to leaving no child behind.

We know the law has flaws, but we also know that with common-sense changes and adequate resources, we can improve it by building on what we've learned. We owe it to America's children, parents and teachers to reinforce our commitment, not abandon it.

We need to strengthen our academic standards and assessment methods to ensure that students have the knowledge and skills necessary for today's knowledge-based global economy. We can improve accountability by helping states modernize their curriculums from prekindergarten through high school so that all students graduate with the education they need to pursue a college or technical degree, participate in the workforce or serve in the armed forces. We should also help states develop better assessments to track the progress and growth of all students, including students for whom English is a second language and students with special needs.

We must expand and fortify the teacher workforce. Researchers agree that teacher quality is the most important factor affecting student achievement. Good teachers can make all the difference in closing achievement gaps for low-income and minority students. The same research also shows, however, that our most at-risk students are often taught by the least-prepared, least-experienced and least-qualified teachers. The No Child Left Behind Act made a commitment that every child would be taught by a highly qualified teacher. To reach that goal, a greater federal investment is needed.

Finally, we can't just label schools inadequate. We must help them improve. States and localities need to initiate and support school improvement. Part of the act's promise was that greater accountability would be accompanied by greater support. We knew that federal resources would be critical to achieving the goals. When the law was adopted in 2002, Congress delivered $22 billion to support public education — an increase of 20 percent over the previous year. This was an unprecedented federal investment. The law promised increased funding levels over the life of its provisions, in step with the increase in targets for student performance. Yet year after year, the federal government has failed to provide the resources that states and school districts need to improve struggling schools. Assessment and accountability without the funding needed to implement change is a recipe for failure.

In the weeks ahead, those opposed to doing what it takes to leave no child behind will do everything in their power to impede our progress. Don't let their rhetoric fool you. Local control means nothing without the resources for improvement. Increasing flexibility without preserving accountability is fiscally irresponsible and educationally unwise.

No Child Left Behind is not just a slogan. It's a national commitment, inspired by our fundamental values and aspirations. It's a promise to do all we can so that every American child receives the high-quality education he or she needs and deserves. We may never achieve that lofty goal, but if we hope to keep America strong and just, prosperous and free, we can never stop trying.

Sen. Edward M. Kennedy, D-Mass., was a lead author of the Leave No Child Behind Act. He wrote this commentary for The Washington Post.