He said Kaye made the commitment to extend it to all Auckland schools on the spot at a meeting with Auckland principals and the Ministry of Education was still working through details, such as whether beginner teachers who are already working in Auckland schools might be able to claim the bonus retrospectively.
"Generally speaking we don't do retrospective payments, however she is going to look at that issue as part of the wider review," the spokesman said.
He said Kaye also told the Auckland principals that the amount of the bonus would be reconsidered in the review.
Since it was announced in 2009, the scheme has paid $3500 for each of the first five years that a beginner teacher spends in a decile 1 or isolated school, provided they stay in the job for at least three years.
The primary teachers' union the NZ Educational Institute (NZEI) complained on Monday that the scheme had not been promoted.
Former Education Minister Anne Tolley said in 2009 that "close to 1800 teachers may be eligible this year".
But only 283 beginner teachers received the incentive payment in 2012, and that number has dwindled in every year since then to 131 last year and only 59 so far this year.
Tolley budgeted $19 million for the incentive for the first three years. But spending peaked at only $2.7m in 2012 and fell to $1.2m in 2013, $1m in 2014 and $560,000 in 2015. Spending figures since then have not been provided.
Extending the scheme to a further 300 teachers starting in 2018 would cost $3.15m at the end of 2020, when they would qualify for their first payments of $10,500, and $5.25m a year after five years if all teachers stay in their jobs for that long.
Bush said it would make "a huge difference" for Auckland schools that are struggling to find staff, with 80 primary school vacancies across the region at the start of this term.
"It means we may not lose as many teachers out of Auckland, and we might be able to attract some into Auckland from the Waikato and further afield," he said.
However, he said some decile 1 principals were disappointed because they would lose their advantage in attracting beginner teachers.
All teachers at decile 1 and 2 schools with "priority staffing" status get an extra $1500 a year, but that is much less than the $3500 a year in the voluntary bonding scheme.
NZEI president Lynda Stuart said Kaye's decision to extend the scheme just days after the union raised the issue was "a great win".
"This only happened because of the thousands of teachers who contacted NZEI and the Ministry of Education to inquire about the scheme since we revealed on Monday that the Government had kept it virtually under wraps for years," she said.
"It's great that the minister is looking to some solutions for the Auckland teacher shortage, but there still needs to be an additional incentive for teachers in low-decile schools which have the hardest job recruiting and retaining staff."
Labour education spokesman Chris Hipkins said he would also look to widening the voluntary bonding scheme if Labour wins next month's election.
Labour has allocated an extra $40m over four years for measures to ease the teacher shortage including "increasing the availability of bonded scholarships in areas of identified teaching shortages, including science, maths, Te Reo Maori and in specific locations".
