New Zealand's poorest high schools will lose thousands of dollars each year because of a Government policy billed as helping more children to play sport.

Prime Minister John Key went to Bairds Mainfreight Primary School in Otara this week to launch the Kiwisport programme in front of a line-up of sporting heroes.

But neighbouring Papatoetoe High School calculates it will be $8000 worse off, and other low-decile schools in the area face similar cuts of about 25 per cent.

Principal Peter Gall said Papatoetoe's funding for sports staff would fall from $41,000 to $33,000 because the new money was not linked to a school's decile rating.

He had spoken to a few other local principals, who had also assumed at first they were about to get more money.

Tangaroa College was down by $7500 and Otahuhu College had lost $6000.

"It seems that we're robbing the poor to pay the rich," said Mr Gall, who is also president of the Secondary Principals Association.

"It's quite ironic that the announcement was made at a South Auckland school and a large number of South Auckland secondary schools are going to be considerably worse off under this policy."

Mr Key launched Kiwisport on Tuesday in front of Olympic champions Sir John Walker, Sir Peter Snell and Hamish Carter and All Black coach Graham Henry.

He described the policy as delivering on National's promise "to put more money directly into the frontline to help more children participate in organised sport".

The programme uses $20 million of money cut from other areas, including anti-obesity programmes and media campaigns promoting exercise.

It gives $6 million to primary schools, $6 million to secondary schools and $8 million to regional sporting trusts to distribute to sports activities for school-age children.

But nearly all the secondary school money comes from an existing $5.3 million annual grant, which pays for sports co-ordinators and is weighted towards lower-decile (poorer) schools.

Mr Gall said Papatoetoe High, which is decile 3 on the 1 to 10 scale, used the money to employ a sports co-ordinator and sports administrator, who were "absolutely invaluable".

The board would have to consider if it could find the money to pay them from other sources. If the school had to cut their hours, it would lead to fewer students getting involved in sport - the opposite of what the Government claimed the policy would achieve.

Mr Gall said he intended to write to the ministers involved to complain about the decision.

A spokesman for Sports Minister Murray McCully said the old policy was changed because it did not give secondary schools enough flexibility.

Officials at wealthier schools who spoke to the Weekend Herald said they had not yet had a chance to calculate how much they would get from the new programme.

Auckland Grammar headmaster John Morris said it was too soon to say what effect the funding changes might have on his school's "massive" investment in sports.

"We run 400 sports teams here at Grammar a year. So you can imagine what that costs us ...

"There's a huge amount of money we put into it so anything we get from the Government above what we'd be getting already, we would welcome."