SAN JOSE -- Nearly seven weeks into the school year, the Alum Rock Union School District will eliminate 18 teaching jobs, move some students to different classes and schools, and create 25 combination classes, as it trims spending to conform to enrollment.

The student population is down 211 students from projections, and more than 500 students down from this time last year, interim Superintendent Stephen Fiss said. The changes will save $1.2 million and affect all of the district's 23 elementary schools, he said.

The district is notifying parents of changes this week, and all the targeted students and teachers will be moved by Oct. 15, he said.

Student enrollment has dropped across the board, with more of the decline in primary grades, Fiss said.

Because the district relies heavily on state funding, which is awarded based on student attendance, when enrollment falls so does revenue.

The bulk of the jobs eliminated, 13, are positions the district has left vacant. Five other classes that are being dissolved have been staffed by substitutes, who will be let go. Two more teaching jobs technically will be erased from the district's general-fund ledger, but the teachers and classes will be paid from a different funding pool, Fiss said.

Administrators worked with the teachers union for several weeks to realign classes with enrollment, this year at 12,300 students. The time lag is due to the district moving carefully. "We don't want to move students and create combination classes unnecessarily," Fiss said.

The district has been hit by fewer births within its East San Jose borders, more families with children moving out than moving in, and the steady growth of charter schools in the district and nearby.

"When you have 20 elementary schools and some mobility in the district, it's sometimes hard to project enrollment precisely," said Jocelyn Merz, president of the Alum Rock Educators Association.

Other than adjusting classes, she said, "it's the smoothest start to a school year and the most positive in many years."

The district previously has moved teachers, students and classes about this time of the year, to adjust for fluctuating enrollment, she said. And the district often notified families on a Friday that their child would change classes on the following Monday.

The neighboring Franklin-McKinley School District, which also serves a large poor student population, moved nearly 200 students a few weeks ago, Superintendent John Porter said. But unlike Alum Rock, enrollment in Franklin-McKinley is growing about 2 percent a year, and this year kindergarten enrollment is at an all-time high -- 140 more students than expected, Porter said. The district provides busing for students transferred away from their neighborhood school.

This year, Fiss said, because future funding is so uncertain, the district is minding the budget carefully. "There aren't a lot of extra dollars around," he said.

And with revenue dependent on tax initiatives on the November ballot, "We have to continue to monitor our budget and staffing," he said. With every fiscal decision the district makes, compared to past years, "the impact is more significant."

Contact Sharon Noguchi at 408-271-3775. Follow her at Twitter.com/NoguchiOnK12.