PRIVATE tutoring colleges have reported a surge in demand to help students prepare for NAPLAN tests and are calling for formal recognition as part of mainstream schooling.

But principals say tutoring defeats the purpose of the National Assessment Program literacy and numeracy tests, which are designed to identify learning difficulties children need addressed. The principals say tutoring would only mask the problems of students needing extra help from teachers.

Mohan Dhall, the chief executive of the Australian Tutoring Association, said NAPLAN tests had opened up a commercial opportunity, with publishers selling books with practice questions for the tests.

''There has been a huge surge in tutoring for NAPLAN in the last 12 weeks,'' Mr Dhall said.

''Mainstream education should recognise private tutoring [colleges] and benchmark them. Up to 30 per cent of family income is spent on [private] tuition. Let's come out of the shadows and be more transparent.''

The president of the NSW Secondary Principals Council, Jim McAlpine, said the publication of NAPLAN test results on the Federal Government's My School website had made them a high-stakes measure for schools.

This had put greater pressure on parents to spend money on private tutoring to ensure their children performed well in the tests.

''The fact that how well schools are performing is being talked about … has made some parents feel they need to hothouse their students on the NAPLAN tests,'' Mr McAlpine said.

''Tutoring for NAPLAN will defeat the purpose of the tests and won't assist the students with learning. The more the results get distorted the less useful the test results will be for giving accurate feedback on what students need to do.''

A spokesman for the NSW Minister for Education, Verity Firth, said public school students were ''taught everything they need to know to perform well in NAPLAN tests in school time. Any decision to send children to a tutor is a private matter for parents.''