Bill English has slammed Jacinda Ardern's decision to ditch the Better Public Services targets which were started under the National Government.
He said it would cause the public service to drift.
"The reason we stuck to them and developed them and the public service started to like them is because when they turn up, they know what it is they are meant to be doing," English told the Herald.
"And if you take them away, they will stop focusing and they will continue on in a fog of good intentions without digging deeply into the problems they are meant to be solving."
Just when the public service was ready to take the next steps to "really dig into the hard core drivers of deprivation" the new Government was going to take the pressure off.
Better Public Services were introduced in 2012 to set out specific targets to reach in priority areas by 2017 - and the targets were revised last year.
Some of the targets included cutting the youth crime rate by 25 per cent, reducing working-age beneficiaries by 25 per cent, reduce rate of initial hospitalisation for rheumatic fever in children, and an increase to 85 per cent the percentage of students who leave school with NCEA level 2 or equivalent.
About two thirds of the targets were met, and some fell short.
Ardern told reporters at Labour's caucus retreat in Wairarapa that the new Government would not be continuing with them.
It would set milestones in some areas and it would set target to reduce child poverty. But she cited the target to reduce rheumatic fever as failing to target the causes of the illness - poor quality, damp housing.
English said the rheumatic fever target was a good target.
"It meant that if part of the problem was housing, you had to act on that specific family and that house.
"Of course there is a role for making sure the quality of all housing is high. But you've got actual kids showing up at the emergency department tonight who are sick and the target forced people to deal with that.
Without targets, money was wasted on "churn" - "turning up 15 times to the same family but not actually changing anything".
The targets made the public service staff understand what they should be doing, who they were doing it for and what difference they made.
"They don't sit round in these endless processes of writing strategies and talking about high-level good intentions and wondering what they are there for.
"That is what the public service will do if they can."
English said the targets also helped to identify the Government's priorities to a detailed level.
English said a lot of public servants would be disappointed the Government was going to ditch Better Public Services.