Critics yesterday assailed the city’s Department of Education for turning public schools into “test-prep factories” and compelling many students to take a standardized test as often as once every three weeks, according to a new analysis of the city’s testing schedule.

A report by the public advocate, Betsy Gotbaum, shows that only two of 12 tests that third- and fourth-graders take annually are required by law. The rest are city-mandated assessment tests that prepare students for state tests. Eighth-graders take between 11 and 12 tests a year, or one every four weeks, according to the report.

“The DOE is trying to take credit for improving test scores, but all they are doing is teaching kids how to take tests,” Ms. Gotbaum said at a press conference.

Last month, students in New York City also showed virtually no gains on the National Assessment of Educational Progress, known as the “nation’s report card,” Ms. Gotbaum said.

Students and parents yesterday urged the city to focus more on subjects that do not appear on standardized tests, such as history, arts, dance, and geography. “We should focus on developing well-rounded students with a complete education, not just creating a generation of professional test takers,” a member of the Community Education Council for District 22, Christopher Spinelli, said.

The president of the teachers union, Randi Weingarten, said in a statement that a growing number of teachers said excessive focus on standardized tests was harming students’ full development.

A spokesman for the education department, Andrew Jacob, defended the testing and said the city used no-stakes evaluations in reading and math to keep track of student progress throughout the year. “In trying to make a bogeyman of testing, the public advocate appears to oppose every measurement of student progress the city might administer from preschool through 12th grade,” Mr. Jacob said in a statement.