By most measures, Midwood High School is a shining example of a successful urban school: it has one of the highest graduation rates in the city, a yearly crop of Intel science award semifinalists, and a college night so packed with recruiters that booths fill both gymnasiums and the cafeteria. Earlier this year, it was listed as one of the city schools successful enough to be exempt from a new citywide curriculum.

But this week, Midwood, in Brooklyn, found itself on another list, along with 496 other city schools that the state's Education Department says failed to meet federal standards under the No Child Left Behind law. It was, said the Midwood principal, Steve Zwisohn, ''almost like a little slap in the face.''

No one argues that the state's list of schools, 374 of which receive federal poverty money, includes many with a range of profound problems. But the appearance of schools like Midwood on the list illustrates what education experts on both sides of the political divide have been saying for months: that the federal No Child Left Behind law is holding up a yardstick that has never been used before.

For the first time this year, schools across the country are being examined not just for what they do for the bulk of the student body, but what they do for particular groups, including black, Hispanic and poor students, and those with disabilities. If one group is found lacking, the school is placed on the list.

At Midwood, for example, a group of 33 students with disabilities -- students who started as freshmen in the fall of 1999 -- failed to show they had made progress on math and English examinations. Those scores got Midwood on the failing list.

''The law makes it impossible to hide behind averages,'' said Dan Langan, a spokesman for the federal Department of Education. ''It is possible for a school to have a relatively high average, but when you look at the disaggregated data, some students aren't receiving the quality of education that they should.''

Throughout the city, news of the state's list, which includes about 40 percent of the city's 1,200 schools, hit hard, particularly as it coincides with the first week of school under a new, restructured system run by Mayor Michael R. Bloomberg and Schools Chancellor Joel I. Klein.

Some principals, who had always considered their schools successful, were left wondering why they were placed on the list. The state provided some information on a few schools to The New York Times yesterday, but most schools were left in the dark.

Last year, the state's Education Department identified 331 New York City schools in need of improvement, all of which receive federal poverty money. Students at those schools, under No Child Left Behind, must be allowed to seek transfers to other schools or, in some cases, be offered supplemental services like tutoring and online classes.

This year, the state added 43 schools to that list. It also named 123 schools that do not receive federal poverty money and whose students are therefore not eligible for such transfers. Schools in both groups must come up with plans for improvement. Last year, states were not required to break down student performance by subgroup.

Jill Chaifetz, executive director of Advocates for Children, a nonprofit group, suggested that the list was so long because of the combination of strict state educational standards with the new federal standards, some of which she described as ''nonsensical.''

Saying that although New York ''has some of the highest standards in the entire nation,'' the new rules put many of state schools ''under failing status when that really may not be the case at all.''

The federal law tells states that they must measure the success of ethnic and other smaller groups within a student body, and it sets a standard for ''adequate yearly progress,'' but states come up with standards for judging success on their own. So New York, which has high standards, may have a larger list of schools on its list than other states with worse schools.

Jill Levy, head of the principals' union, used the word ''schizophrenic'' to describe the standards that yielded the state's new list. She pointed to the example of Hillcrest High School, in Queens, which was listed as a ''school in need of improvement'' even after being designated a New York State Blue Ribbon School of Excellence. Hillcrest was placed on the list after the state found that its general population had failed to improve in English and math test scores.