Mayor Bill de Blasio is abandoning his predecessor's controversial system of letter-grading each city public school in favor of more nuanced metrics that give less weight to standardized tests.

In place of A-to-F grades for the city's more than 1,800 schools, a Bloomberg-era policy in place since 2006, each school will be evaluated on a mix of questionnaire answers, objective metrics and in-person observations by experts. The policy will be fully implemented next year.

Chancellor Carmen Fariña, speaking during a policy address Wednesday morning in the auditorium of Brooklyn's PS 503/PS 506, said the letter grades were neither useful nor informative in helping parents evaluate how well a school served its students.

"They are not restaurants," she said, a reference to letter-grading of eateries' sanitary inspection results, which former Mayor Michael Bloomberg's administration also introduced in the city.

Fariña's announcement is yet another education policy shift for the de Blasio administration from Bloomberg's. Other moves have included a reduced emphasis on charter schools, an overhaul of teacher evaluations and a labor settlement with the teachers union.

In jettisoning the letter grades, de Blasio's Education Department conceded that the new system is much more complex but gives more accounting of what makes a good school.

Jeremiah Kittredge, chief executive of a pro-charter-school group Families for Excellent Schools, criticized the policy switch.

"With more than 143,000 students trapped in failing schools, Chancellor Fariña chose today to go backward, refusing to acknowledge failure and rejecting accountability," he said.

The new school-assessment system includes answers to questions such as "How well do teachers work with each other?" and "What is it like to be at this school?" The system tracks student progress on credits, Regents, graduation and test scores but doesn't distill those indicators into grades.

Under the Bloomberg system, schools received "progress reports" -- an overall letter grade, mostly based on test scores, and individual ones in each of several categories.

Parents will see a preliminary report later this year, with the full changes by next year, Education Department officials said. It will be available online or by request on paper.

Lisa Sarnicola, one of the principals who hosted the chancellor, called the changes "what our schools need."

"The big thing is the trust factor," said Sarnicola, whose school received an A last year under the Bloomberg system. "It should not just be about tests. It should be about what goes on each and every day within the school building."