NEW YORK — Thanks to heavy parent involvement and high test scores, Public School 321 in Park Slope, a well-off neighborhood in Brooklyn, is considered a gem of New York City's public school system.

In the eyes of New York's Department of Education, however, P.S. 321 deserved just a B in the city's first school report cards, which are based largely on how students score on standardized tests.

Such accountability efforts — widespread since the advent of the federal No Child Left Behind Act — have raised the hackles of parents and teachers across the country, who fault the methodology and question the wisdom of tying test results to the job safety of teachers and principals.

Now some parents in the nation's largest school system are voicing similar concerns about the grades, released in November as part of Mayor Michael Bloomberg's push to turn around underperforming schools.

"It really saddens me that this is how the Department of Education thinks that parents are best served, by boiling everything that happens in an entire school to a letter grade," said Lee Solomon, the mother of a first-grader at the Brooklyn New School, a sought-after school that accepts students only by lottery but got a C.

Teachers have debated the push toward testing since No Child Left Behind was enacted in 2002 at President Bush's urging. While some studies show that student achievement in reading and math has increased, teachers complain that they are forced to "teach to the tests" and give up "frills" such as music, art and recess.

A 2006 survey by the Washington-based Center on Education Policy found that since the passage of the federal law, 71 percent of the nation's 15,000 school districts had reduced the hours spent teaching history, music and and other subjects to open up more time for reading and math.

Bloomberg, who is considering an independent presidential run, won mayoral control of schools in 2002 and has sought to make education reform a key part of his legacy.

James Liebman, chief accountability officer for New York City schools, devised the grading system for the city's 1.1 million-pupil school system. Liebman said standardized tests are a good measure of whether students have learned what they should know.

"If children can't read and they can't do math, then the educational system and their school have failed them," he said.

For New York's middle and elementary schools, 85 percent of the grade is based on performance on standardized tests, while high schools are judged on graduation rates, New York State Regents exam scores and other factors.

Liebman pointed to a Quinnipiac University poll in which voters said the grades were fair by a margin of 61 percent to 27 percent.