The 2002 No Child Left Behind Act focused the country’s attention on school reform as never before, but the law is far from perfect. The Obama administration is wise to address its flaws, since Congress is four years overdue in updating the law.

The Department of Education’s plan gives states that agree to several reforms — including stringent teacher evaluation systems and new programs for overhauling the worst schools — an exemption from many of the law’s requirements. It would permit the states to change the way they evaluate most schools for the purpose of compliance, allowing indicators other than just reading and math scores to be considered. And it would lift the law’s provision that all students be proficient in math and reading by 2014, which was never going to happen anyway because there were so many loopholes.

The administration, however, must not allow the new waiver system to become a way for states to elude the purpose of the act, which is to raise student achievement across the board.

The waiver plan will cure several obvious shortcomings of the original law. It would allow schools to be rated partly on achievement-growth measures — how much students improve on reading and math — instead of just on the percentage of students who reach “proficiency” on those tests. The current approach has led many schools to ignore both high-achieving and low-achieving children to focus on pushing up students who fall just short of the proficiency mark.

It would also put an end to the much despised pass-fail system under which otherwise high-performing schools are rated as “needing improvement” if one racial or economic subgroup falls short of yearly achievement targets. And it would allow districts more flexibility in the use of federal dollars.

To qualify for waivers, states will have to install new tests — and teacher evaluation systems that take those test results into account — by the 2014-15 school year. The 12 states that received federal grants in the Race to the Top program last year have a head start. They agreed to put in data-driven teacher evaluation systems as part of that competition. But even reform-minded states like Delaware, which was one of the first to win a grant, have been unable to get their systems up and running and have asked the government for more time.

Part of the problem is that in most states, yearly math and reading tests are given only in grades three through eight and once in high school and cover less than half of the teachers. This means that the system must devise other rigorous rating measures for the remaining staff. Another is that the systems must be designed not just to show how much children have improved, but also to provide guidance so that ineffective teachers get better.

It seems imprudent to rush the states into bringing these complex new evaluations systems and high-quality tests on line by 2014, given that they will also be expected to adopt new core curriculums.

The Obama administration must insist that states getting waivers demonstrate that they are making substantial progress, but it should allow flexibility on the timing. Having states rush to adopt inadequate evaluation systems would discredit the school reform movement.