Sensitive pupil information is vulnerable to theft from school networks, official guidance says, undermining plans to give families home access to school records.
The Government is set to announce a multi-million pound deal to provide laptops and broadband access to the million poorest homes.
But schools will not be able to provide families with full access because Becta, the education technology agency, has ordered a tightening of pupil data security in light of recent security breaches.
"Until new technology or enhancements to your existing ICT infrastructure can be put in place, you are likely to need to make operational changes," the Becta guidance says. "This may mean that certain types of sensitive data may no longer be accessible away from the school in the short term."
Last week, a memory stick containing sensitive files on 10 children with special educational needs (SEN) was found, unencrypted, at a Somerset service station.
The Becta guidance, to be published this month, states that protected data must be encrypted before it can be removed from a school. Protected data may include assessment records, medical and special needs information. As an example, sensitive SEN data could only be sent to parents who have two- factor authentication and via password-protected files.
"Failing to apply appropriate controls to protect this data could amount to gross misconduct or even legal action," Becta warns.
Paul Shoesmith, its technical strategy director, said the need to keep children safe was paramount.
"This is serious," he said. "There is data in school systems which, if it were lost, could . result in harm coming to children. That is not an acceptable risk."
But Valerie Thompson, chief executive of the e-Learning Foundation, who has been working for seven years to persuade ministers to fund home access for families, said: "It would be a shame if schools were not able to provide this information. But you can understand how sensitive the Government is about more leaks of personal data."
The Becta guidance threatens to undermine its own Next Generation Learning campaign to get parents to "demand" effective 247 learning technology from schools.
Becta believes that only one in five schools uses technology effectively. It plans to work with big retailers to convey to parents the importance of home access to their children's learning.
Stephen Crowne, Becta's chief executive, said: "We need to encourage learners and their parents and carers to understand the benefits of technology, and really demand those benefits from their local school."
FREE LAPTOPS FOR 1M MOST DEPRIVED
All seven million households with children should be able to link to schools online by 2013, Jim Knight, schools minister, says.
The Government is set to announce a plan to give deprived families with children a free laptop.
The pound;250-pound;300 million scheme is expected to be part of Gordon Brown's bid to reassert his credentials, so is likely to be unveiled at next week's conference.
Mr Knight told The TES that home internet access could make an enormous difference to children's learning and to families' ability to access public resources.
"It means half a grade on GCSEs, finding savings on utility bills, allowing parents to log on to the school intranet to see their children's reports," he said.
"That's why I'm working hard with officials to close that digital divide."