Mayor Bloomberg called for an end to social promotion for the city’s fourth and sixth graders this morning, a change that would expand one of the most hotly debated education policies of his tenure.

At a press conference this morning, the mayor and Chancellor Joel Klein called their efforts to end social promotion “a great success,” citing rising test scores and the decreasing number of students enrolled in summer school. Ending social promotion means that students who do not meet proficiency standards on state tests are held back until they do. Some of these students attend summer school and are bumped to the next grade in the fall when they pass the exam, while others can have waivers signed that let them out of retention program.

Bloomberg said that once the citywide school board is reconstituted, he would ask it to end the policy in grades four and six — the only remaining tested grades in which social promotion is still in practice. In 2004, when several board members told the mayor that they would vote against ending third grade social promotion, he had them removed and replaced overnight with people who supported his policies. The event is commonly known as the “Monday Night Massacre.”

Standing in the library of the Patrick Henry School (P.S. 171) in East Harlem, Bloomberg said that with the new retention policy, “kids will either learn what they need or teachers will know they haven’t learned.”

Asked about researchers’ claims that retention policies can raise the dropout rate, Bloomberg said he was “speechless,” adding, “It’s pretty hard to argue that it does not work.” Klein said that since 2004, when the DOE ended social promotion for third graders, support for its end has been “unanimous.”

There is significant opposition to the administration’s retention policies, said Norm Fruchter, director of the community involvement program of the Annenberg Institute for School Reform.

“The opposition to ending promotional policies in the research community is universal and overwhelming, so where he gets the idea that the support is unanimous is another thing he manufactures out of his head,” Fruchter said. In 2008, when the chancellor ended social promotion for eighth graders, Fruchter suggested that the city wait until it had developed successful programs to support the students it held back.

City officials said an “enrollment snapshot,” taken the Thursday before state tests were given this year showed there were 105,531 students in summer school, compared to 119,954 in the same week last year.

“In some respects it’s a moot point because there are so few students scoring at level 1,” said Jennifer Jennings, a doctoral student at Columbia University whose analysis of state math tests showed that the questions have become repetitive and easier than in previous years. Jennings said that with test scores rising across the state, fewer students scored low enough to be held back.

The Bloomberg administration said that fewer students need to attend summer school, not because the tests are easier, but because the retention policies are working.

According to a press release from the mayor’s office, “Students who must repeat a grade under the policy are also far better prepared for future work.” It noted that third, fifth, and seventh graders who repeated a grade met proficiency standards or higher when they moved onto the next grade.

It’s unclear how students held back since Bloomberg began the policy in 2004 have fared, as there is little independent data. A report by the RAND Corporation on ending social promotion, which was commissioned in 2004, still has not been made public.

As for whether the Panel for Educational Policy will approve the measure, the mayor said it was “just a hypothetical that they wouldn’t.”