Average class sizes increased by 1.6 percent this fall – from 26.3 to 26.7 students per class – an increase of 0.4 students per class, according to a preliminary report by the Department of Education.

First grade experienced the biggest jump, going up by nearly a whole student per classroom – from 23.9 to 24.8. Elementary school class sizes increased on average by 0.4 students, from 24.4 last year to 24.8 this year. The D.O.E. said there were enrollment increases this year in kindergarten, first, 7th and 12th grades.

Middle school class sizes went up from 27 to 27.3 students per class, and high school class sizes increased from 26.3 to 26.8 students per class. The city looks only at English, math, science and social studies “core classes” in high schools.

Data on the D.O.E.’s web page includes a breakdown for individual schools.

United Federation of Teachers president Michael Mulgrew released this statement:

“Every parent and every teacher knows how critical it is that classes are small enough that each child can get individual attention. But Mayor Bloomberg disagrees, and since 2007 New York City class sizes keep getting bigger and bigger. It’s time for the DOE – with its legions of ‘accountability’ officers and hundreds of lawyers – to focus its attention and budget resources on the schools, not the bureaucracy.”

The D.O.E. said nearly half of all schools had no or minimal increases in class sizes. Noting that school budgets were flat this year, the department said some schools may have “experienced adjustments in their budgets depending on changes in their student and staff composition.”

The number of classroom teachers, excluding those teaching self-contained classes, decreased by 67 positions from 58,981 to 58,914, according to the D.O.E.

Overall, the number of classes with special education students continued to grow in response to a city policy. Those classes often have more pupils than general education classes but they also have two teachers, effectively reducing student-teacher ratios.

The information was released Friday afternoon, just as news of the mass shooting in neighboring Connecticut was getting out. The D.O.E. noted that under law, the report was originally due by November 15th but that the city council extended it to Dec 14th to allow the agency to prioritize hurricane recovery efforts.

The D.O.E. is required to release reports on class size twice a year, with a preliminary report in November and a final update in February. The city uses early data collected by the schools as of Oct. 31, but this year’s data was for Oct. 26 – the week before Sandy struck and closed the schools. The D.O.E. emphasizes that preliminary data is just that, because it can include long-term absences.