by Donna Krache, CNN

(CNN) Sequestration: The word strikes fear in the hearts of school boards and administrators nationwide, and with good reason.

What does it mean? The term refers to the across-the-board budget cuts that will automatically occur in federal programs in January 2013, unless Congress reaches an agreement by the end of this year on reducing the deficit.

What kind of cuts will this mean for education?

The American Association of School Administrators (AASA) estimates the reductions would amount to over $4 billion. That would plunge education funding into pre-2003 levels, according to the National Education Association.

Why is that so scary? Part of the reason is that America’s schools have added 5.4 million new students to their rolls since 2003, and costs have risen about 25%. Budget cuts triggered by the fiscal cliff could potentially affect millions of students and teachers by reducing programs and services and increasing class sizes.

According to Deborah Rigsby, director of federal legislation for the National School Boards Association, if sequestration happens, each school district could lose more than $300,000 for every 5,000 children enrolled.

“Sequestration would hurt our school districts and ultimately, our students,” said Rigsby on a conference call Wednesday.

Not all of the effects would be immediate, although some federal programs, such as Title I, Head Start, and state special education funding would feel the impact of the cuts right away. Schools that receive Impact Aid funding would also experience immediate cuts.

Schools would really feel the hit next academic year. According to the National School Boards Association (NSBA), sequestration won’t automatically impact most schools’ 2012-2013 budgets, but for the 2013-2014 school year, the impact could be “profound.”

A U.S. Senate subcommittee warns that cuts would spell out layoffs for more than 46,000 employees nationwide, unless states or communities covered their salaries.

But many states and school districts may not be able to help. In an AASA surveypublished in July, state and local districts were asked if they’d have ability to soften the impact of sequestration. Some 90% of them said they didn’t – that their state would be unable to help absorb or offset the cuts.

“We love our public education here, but we feel like we’re under attack,” said Juandiego Wade of Virginia’s Charlottesville City Schools on the NSBA conference call. “We don’t have the resources to supplant those federal funds.”

Already out of reserves drained during recession years, states would have to respond by reducing teachers’ professional development, programs such as after-school and enrichment, and personnel, according to the survey. Also on the table: Deferring textbook and technology purchases and reducing extracurricular activities.

Some schools are bracing for impact.

A little more than half of the school districts that responded to the survey say that they have built some cuts into their 2013-2014 budgets to offset sequestration. A little less than half say they have not and plan to address the cuts when they happen.

Board member Jill Wynns of the San Francisco Unified School District California would lose $387 million in education funds in the first year alone of sequestration. And that’s on top of 20-24% cuts the state has already made to its education budget since the 2007-2008 school year.

“This is not saving money. It’s disinvesting in our future,” said Wynns.

Education advocates and organizations have launched massive efforts to put pressure on the president and Congress to prevent sequestration.

The National School Boards Association has reached out to Congress and raised awareness among its members, giving them steps they can take to help stop the cuts from happening.

The National PTA has a sequestration toolkit to provide its state and local units with information as well as templates for letters to Congress and media outlets to turn the pressure up on elected officials.

On the NSBA call, the Virginia school board member reflected on the recent elections and spending priorities.

“Our state saw a lot of campaign money spent here last month. I wish some of it could be spent now on education,” said Wade.