A report from the Independent Budget Office is heightening concerns that the city has kept public school classes large in spite of nearly $200 million in state and federal funds dedicated to making them smaller.

Classes did become smaller on average last year, but the drop — to 25.71 students in a class from 25.92 in fourth through eighth grade, and to 21.06 from 21.12 in kindergarten through third grade — was small, the report said.

Sixty-three percent of younger students were in classes with more than 20 pupils, the state-recommended target for those years.

And rather than create more classes to alleviate pressure on students and teachers, as advocates have demanded, the number of classes offered in the public schools actually dropped by 158 students in lower grades and 303 in fourth through eighth grades, the report, which drew on final city registers, showed.

An enrollment drop of nearly 15,000 students explains the change, a spokeswoman for the Department of Education, Debra Wexler, said.

Even fewer classes would have been offered had it not been for the extra funding, which the city used to hire 1,006 new teachers and create 1,611 classes last year, Ms. Wexler said.

The president of the teachers union, Randi Weingarten, called the report “disturbing.”

An advocate of smaller classes, Leonie Haimson, said the report reiterated the conclusion of a 2006 audit by a state comptroller, Alan Hevesi, which found that the city’s class size reductions were so small they violated state law.