Senior White House officials have warned schools to prepare for mass absences and emergency closures as they draw up plans to keep lessons going if a bird flu pandemic hits America.
Schools may have to provide tuition over the internet or via post, radio or television, as their buildings are closed or turned into makeshift hospitals or quarantine sites.
Margaret Spelling, US education secretary, said: "Health experts predict illness rates at the height of a pandemic will be highest among school-aged children - possibly 40 per cent."
Experts fear schools will provide ideal conditions for bird flu to spread, because they hold large numbers of people and are notorious breeding grounds for cold and flu viruses.
They also fear that children will be among those most susceptible to infection, making schools central to planning for an outbreak among people.
"Schools must prepare for a number of contingencies, including staff absences, closures, caring for students and the possibility that they may need to be used as makeshift hospitals and quarantine or vaccine sites," Ms Spellings said.
"If we wait until the first human-to-human transmission to get serious about our response, it will be too late."
Tom Skinner, spokesman for the US government's Centers for Disease Control, said: "We can't say with certainty children would be more affected, but, judging from traditional seasonal influenza, the young, elderly, and people with compromised immune systems tend to be (hardest hit)."
He said viruses can spread very quickly through schools, where there are lots of people in close proximity, through coughing, sneezing and contact with contaminated surfaces.
Schools need more than ever to stress the importance of hygiene, such as hand-washing, and of staff and students not coming in if they feel sick, he said.
Ms Spellings announced special "Pandemic influenza planning checklists" for nursery schools and universities, to complement guidelines for primary and secondary schools issued last month.
The documents call on schools to ensure that children are still taught if disruptions occur, through "web-based distance instruction, mailed lessons and assignments, or instruction via local radio or television stations".
Ms Spellings cited Seattle as a model for how schools must co-ordinate with health agencies in their planning. Pegi McEvoy, safety administrator for Seattle schools, said she meets city health officials monthly.
She said pandemic planning presented unique challenges, for example, how to send home an affected pupil. "Usually we'd put them in a taxi, but this might infect the driver," said Ms McEvoy. Community-wide thinking was needed.
Some health experts also project that a flu pandemic could come in two waves, posing major disruption to the school year, Ms McEvoy said.
In North Carolina, education chiefs recently created a dedicated "taskforce" of teachers, heads and administrators to undertake pandemic planning, said state superintendent of public instruction June Atkinson.
The group is looking into using schools as conduits to get general information about bird flu to parents and the wider community, she said.