Time to put away the flip-flops and dust off the calculators. Summer vacation is officially over.

As students and teachers return to East Bay schools this year, some major changes will greet them: Budgets are tighter, classes are fuller, some courses have disappeared and millions of dollars in construction work is under way.

The fallout from the state's sluggish economy and budget woes hits schools this fall. Although the initial impact is not as severe as officials feared it would be, few schools have escaped the cuts entirely.

On the financial flip side, many districts are flush with construction money from state and local bonds. Some classes and, in the case of West Contra Costa, entire schools have been relocated to portables this year to make way for major projects.

That means inconveniences big and small for students and teachers, from dust and noise to last-minute classroom changes.

At high schools in the Mt. Diablo school district, crews were still installing stairs and wheelchair ramps and connecting electricity on temporary portables late last week, aiming to finish before school opens Wednesday.

"Everybody's calling. Everybody's nervous," said Peder Pedersen, director of maintenance and operation. "We'll be working all the way though the weekend."

Over the summer, the high schools, as well as Oak Grove and Riverview middle schools and Shore Acres Elementary, received new roofs, pavement and paint. Other projects will continue into the school year, including bathroom renovations that will require temporary bathrooms to be installed on campus.

On their first day Tuesday, more than 500 students at Lincoln Elementary School in Richmond had to learn their way around portable classrooms set up on campus. The portables will be the school's home for the year, while the old building undergoes a complete renovation and a new wing is built.

New principal Stephen Riave said it was a race to get the portables ready for school; the last truck pulled away at 7:30 a.m. before school started. It added to the excitement of the first day, he said.

"If it wasn't for the professionalism and patience of our teaching staff, it would be really difficult, but we have a really good group here," he said.

Students have to make do with a playing field less than half its normal size, but the payoff will be big: a school that looks like new next year, Riave said.

After major budget battles last spring, class sizes remain limited to 20 students in kindergarten to third grade throughout the Times coverage area. But classes in higher grades may be fuller than last year, because districts are trying to squeeze every dollar out of their budgets by closing classes with low enrollment.

Middle and high schools in the Mt. Diablo district have tightened up their class schedules to meet a higher staffing formula: one more student per teacher on average than last year. Fewer sections of some classes will be offered, but until schools firm up their schedules, officials won't know which ones, said Alan Young, associate superintendent.

"The classes should be as close to maximum as they can be," he said.

At Pinole Valley High in the West Contra Costa district, the music program was spared severe cuts. But the after-school arts conservatory may have to drop about half of its offerings, because funding from the district, Contra Costa College and the city of Pinole was cut, said band director Ed Nesmith.

Funding for Nesmith's marching band class was also cut significantly. He now teaches the class for almost free.

Other East Bay teachers and administrators face the challenge of providing the same instruction with less funding.

Croce Elementary in Livermore lost its two science teachers, but lab science will continue to be taught at the school, said principal Janet Loughran-Smith. One teacher at each grade level will take responsibility for providing science instruction for all the classes.

"We are going to need parent help setting up and cleaning up," she said. "It's going to take a little work to figure this out. ... But science will go on in the classroom."

Parents at Croce and many other schools are also being asked to contribute more financially to keep programs going at school. Croce parents have already raised about $40,000 for the school and plan to raise more.

Despite the cuts, the first day at Croce went smoothly.

When Loughran-Smith saw excited children pouring into school Wednesday, she thought: "Yes! That's why I'm here. They're darling. I just love having them back in school."