Editor's note: An earlier version of this story incorrectly described state schools chief Jack O'Connell's position on the 180-day school year. O'Connell does not support the governor's proposal to shorten the school year.

Under the governor's latest proposal to balance California's budget, school districts can shave five days off next school year to save money.

The idea is to give districts flexibility to reduce state schools spending by $5.2 billion over the next 18 months.

Educators say the trade-offs between a 180-day school year and a 175-day year are murky; unions have promised to fight before letting their members lose five days of pay.

Throughout the Sacramento region, school officials are mulling their options. Here are questions and answers to help put the issue in perspective.

What is a 180-day school year?

One hundred and eighty is the minimum number of instructional days California requires of its public schools. Some districts have more. The 180 days doesn't include in-service days for teachers.

How would the cuts be made?

School board members could decide to shorten the year for their districts or not. Those that opt for a shorter school year would eliminate the equivalent of five instructional days, either in minutes or actual days.

Can you put the cuts in perspective?

Trimming the calendar by five days roughly translates to 3 percent of the school year, said Brian Stecher, an educational analyst with the Rand Education program.

"It's a relatively small cut, but on the other hand, if we saw academic gains of 3 percent across the state, we'd be very happy," Stecher said.

How long is the school year in other states?

According to the federal government, most states require a 180-day school year. Kansas has the longest year with 186 days. Colorado has the shortest with 160 days.

How would cutting school days save money, and how much?

Reducing the school year to 175 days would save on salaries and operational and maintenance costs. According to the California Department of Finance, the state's 1,000 districts could collectively save $1.1 billion.

When would the cuts go into effect?

During the 2009-10 school year.

Where do employee unions stand?

The California School Employees Association, which represents classified employees including custodians and office staff, and the California Teachers Association are opposed.

"Districts don't get to unilaterally abrograte (union) contracts," said Dave Low, assistant director of governmental relations for CSEA. "The governor is throwing out options that are pretty far-fetched in terms of their capacity to be implemented."

CTA President David Sanchez said in lieu of cutting the school year, his union is proposing a "Public School Investment and Accountability Act," which would create a 1 percent sales tax increase effective Jan. 1, 2010. If approved by the Legislature, it would generate between $5 billion and $6 billion a year for K-12 and community colleges.

Can districts shorten the year without agreement from unions?

It's illegal for districts to unilaterally impose a five-day furlough, said Ron Bennett, president of School Services of California, a leading nonpartisan think tank. But if unions don't agree to the furlough, their members may face layoffs.

Are there academic benefits to a 180-day year?

"No one is able to say with authority that 180 days is better than 175," said Bennett. "There is no data that would be so specific as to differentiate the different (academic achievement) in those five days."

Are there other options for cutting school spending?

In addition to cutting five instructional days, the governor said districts could reduce payments to their reserve and maintenance accounts and use money usually earmarked for specific programs, such as adult education, class-size reduction and child nutrition, for any purpose. They also could eliminate one of two science courses required for entrance to the University of California and California State University systems.

How do the options compare when it comes to student achievement?

"Research doesn't give very many direct comparative insights into instructional time versus class size versus textbooks versus art and music," said Stecher, of the Rand Education program. "At some point, there is no clear research answer to these choices."

How did California settle on a 180-day year?

In 1983, the state ramped up educational funding to increase instructional time, but a longer school year was optional, said Kim Clement, a school fiscal consultant with the state. The official instructional calendar was 175 days, but if districts went up to 180, they received extra money.

The 180-day calendar became mandatory in 2000.

Historically, how many days in a school year?

As public schooling grew in popularity in the mid-1800s, the school year varied across the country. Children in urban areas often went to school 11 or 12 months of the year, while those in the country had shorter calendars, maybe five or six months during the winter. They worked the family farm the rest of the year.

The school year became longer and more uniform at the turn of the 20th century.

Call The Bee's Melissa Nix, (916) 321-1090.