The head of the leading body representing independent schools has accused the Government of "not listening" over plans to store every child's details on an elaborate database.
David Lyscom, chief executive of the Independent Schools Council, said a decision to take ContactPoint nationwide will create "yet another task that diverts schools away from educating children".
Last month, the Government announced it would roll out the scheme to every local authority after it deemed an "early adopter" project in the North West a success.
The #163;224 million database will contain a record of all under-18s England, with their name, address, gender, date of birth and a unique identifying number.
An estimated 390,000 social and health care workers, teachers and police officers will be able to access the data.
But Mr Lyscom says that the information that schools need to provide has not been defined clearly enough.
He is also worried about the bureaucratic burden for private schools, which do not have IT systems such as SIMS for transferring the data to their local authorities.
There are also concerns that the information could fall into the wrong hands, given the Government's record on data loss.
He added that parents in the pilot areas had not always been informed of their right to "shield" sensitive information.
This option is available to children whose parents are employed in sensitive areas such as the military, politics or controversial scientific research.
He told The TES: "A lot of the information hasn't been defined very well, but if our schools misunderstand and get it wrong they are legally liable.
"Schools must provide details of additional services accessed by children. Where does that stop? SEN? The school nurse? Piano lessons?"
He added: "We had hoped that after the early-adopter phase our concerns would be listened to, but they haven't. If we want to make sure vulnerable children are protected we are not convinced this is the best way.
"What we need to ensure is that the different services that are working together are doing so effectively.
"By lumping all the children together on one database we create a lot of clutter."
And Mr Lyscom is not alone in his concerns. The Conservatives and Liberal Democrats are committed to scrapping the scheme, should they win the general election.
But the Department for Children, Schools and Families points to a new report on the early-adopter phase in which 75 per cent of people using the database said it would be useful.
One deputy headteacher quoted in the report said it had enabled him to locate eight students who had been missing from education for more than a year.
ContactPoint was set up in response to the murder of eight-year-old Victoria Climbie, who died at the hands of her guardians in 2000 despite being known to social workers and doctors.