America's public schools are half way to the target date by which all students are required to be proficient in reading and math. According to the No Child Left Behind Act, every student must perform at grade level in those subjects by 2013-14.

The target date and the 100 percent proficiency goal capture the ambition — idealistic, to be sure — of the federal law and the difficulties involved.

The law expects states and their public school systems to ensure that a first-grader can read at first-grade level, and a 10th-grader can do the same at the 10th-grade level, regardless of economic, cultural or physical handicaps.

The rationale for the goal is clear enough. How to achieve it, though, has proved challenging from the start. For one, in the absence of a national system of education, there is no single standard of proficiency. Instead, the federal law requires education officials in each state to submit plans indicating their ''annual measurable objectives.'' The plans specify how the state assesses proficiency and what targets it aims to achieve year by year until it reaches the 100 percent proficiency mark in 2014.

As critics have observed, the No Child Left Behind demand for 100 percent proficiency is a progressive idea — up to a point. The law demands some accountability from school systems, but ''proficient'' is relative, under the circumstances. States set their own assessment tests and determine the performance levels that constitute adequate progress. Studies have noted the varying degrees of difficulty of some state tests and the low standards of proficiency.

In short, easier tests and lower proficiency goals mean some states can reach the 100 percent target on time — and with less effort on their part. It would appear the law has provided an incentive for the very problem No Child Left Behind was supposed to cure: ''the soft bigotry of low expectations,'' as President Bush often has put it.

A study released this month by the Center on Education Policy shows another source of concern. In a review of states' strategies to meet the 2013-14 deadline, the center found nearly half of the states, including Ohio, face a steep challenge to make the target date in the time remaining. Planning the timeline for total proficiency, officials in Ohio and 22 other states set low annual targets in the early years for percentage gains in student proficiency. As a result, they must show dramatic gains in student achievement to be able to make the goal at all.

Ohio has spent many years strengthening the base for student achievement, among other things, overhauling curriculum content and aligning it to the state achievement tests. With all that groundwork, the hope is that Ohio's students now will be able to post gains at double speed.