Even as the schools chancellor increases the importance of using testing data to evaluate students and schools, the city’s top testing official is stepping down.

Lori Mei, who is in charge of analyzing the test scores of the city’s 1.1 million public school children, submitted her resignation yesterday, saying she was ready to move on.

Ms. Mei is the second top official to resign from the Department of Education in the past month. The deputy chancellor of teaching and learning, Carmen Farina, announced her resignation in April.

Since taking control of the city’s public school system, the Bloomberg administration has made testing a central component of its reform effort. The chancellor, Joel Klein,put an end to so-called social promotion by requiring students in some grades to pass state tests before advancing to the next grade.

Ms. Mei became a target of parental outrage when Mayor Bloomberg announced that third-graders would be retained if they didn’t pass the tests.

Education historian Diane Ravitch called Ms. Mei’s departure a “loss” for the school system. “Testing has become front and center. It’s the most important thing happening in the system. Everything that happens in the curriculum and instruction is centered around testing,” Ms. Ravitch said.

While Ms. Mei simply said that she was ready to try something new after 23 years in the system, education analysts speculated that she was unhappy with some of the recent changes being implemented by the new accountability office.

“I’ve been with the department for a long time and I’ve really been honored to be part of the reforms and I’m proud of what I’ve accomplished,” Ms. Mei, 50, told The New York Sun. Now that the state has taken over all annual testing, she said it seemed like a good time to try something new. Asked if she had any criticisms of the new testing initiatives, Ms Mei replied, “I’m honored to have been a part of Joel Klein’s administration.” Ms. Mei, who earns $183,000 a year at the education department, said she did not yet have another job lined up. “She’s a fantastic professional and we’re very sorry to be losing her,” Mr. Klein’s spokesman, David Cantor, said. “The chancellor has been in office longer than any chancellor in a very long time, and it’s inevitable that in the course of his tenure that top aides will leave.”

Since January, several other key education officials have also stepped down, including Mr. Klein’s communications director, Stephen Morello; Ms. Farina’s top aide, Laura Kotch; and two senior counselors, Matthew Onek and Jean Deravines, among others.

Ms. Farina, 63, said that after 40 years in the system, which included years as a teacher, principal, and superintendent, she wanted to time to spend with her grandchildren. The former head of testing for the city, Robert Tobias, who is now an education professor at New York University, said he was surprised to hear about Ms. Mei’s departure.

“The responsibilities are enormous; testing is the coin of the realm,” Mr. Tobias said. “It gets tremendous publicity, and there’s a lot of pressure to not only get test scores right, but the testing program has expanded quite a bit.”

Ms. Mei will officially resign at the end of June.The deputy senior instructional manager for assessment and accountability, Jennifer Bell-Ellwanger, will take her place.