A "big brother" Ofsted survey which asks children as young as 10 if they have been drunk or smoked cigarettes has been criticised by teaching unions.
Pupils in years six, eight and 10 are taking part in the survey
Ofsted says as the survey of 120,000 children in England aged between 10 and 15 was anonymous - parental permission was not required.
But teaching unions say children can be identified from the full postcodes the survey asks them to provide.
Education inspectors insisted these would not be used to identify children.
The inspection watchdog said the results of its Tellus2 survey - covering home life, health and bullying - would be used to help local authorities assess their success in meeting the needs of children and young people.
Pupils in Years 6, 8 and 10 are being asked to take part in the survey, which has a closing date of 14 June.
Questions include: "In the last four weeks, how many times, if any, have you been drunk?"
Participants are also asked if they have smoked cigarettes and if "the dad or step dad you live with has a paid job".
A spokeswoman for the National Union of Teachers (NUT) said the union had concerns over both the nature and the purpose of the questions.
"There are some questions that seem quite personal," she told the BBC News website.
"One has to ask why Ofsted needs to know if pupils have had a drink.
"Just because you have a captive audience doesn't mean you should be abusing that position."
There also seemed to be a lack of assurances about how information was being used, the NUT spokeswoman added.
She said the fact that participants were being asked for their postcodes meant the survey was not anonymous, as Ofsted has claimed.
"A postcode gives you an address," she said.
National Association of Head Teachers' (NAHT) general secretary Mick Brookes said members of his union felt their profession was being undermined by the questionnaire.
"It feels as though big brother is watching over your shoulder the whole time when what we should be doing is taking that away," he said.
He said he knew a number of head teachers who had refused to let their schools take part in the survey.
An Ofsted spokeswoman said the questionnaire was confidential and that participants would not be identified.
"The postcodes will not be made available outside Ofsted and will be used for analysis purposes only," she added.
"Information made available to local authorities will be analysed by the first three digits only and only then when there are enough responses in any particular grouping to avoid identification."
Questions had been tested with children and had not resulted in any negative feedback, she said.
Responses to the more personal questions would help local authorities to "meet the needs of those vulnerable children and young people who need the most support", she added.
She said the survey had been discussed with a number of different agencies and had received "an overwhelmingly positive response".