Proposed changes to teacher training could actually reduce the quality of their work, the NZ Principals' Federation warns.

Education Minister Hekia Parata has announced an education shake-up, including plans for a new system of teacher monitoring which could be used for performance pay.

She says a teacher appraisal system will be developed over the next two years, in conjunction with the sector, to help improve teaching quality.

A post-graduate qualification will be introduced as a minimum for all trainee teachers, while a new pre-principalship qualification will be introduced for principals.

But the Principals' Federation is sceptical of the plans.

President Paul Drummond says a subject-specific degree, followed by a shorter teacher training period, may be suitable for secondary teachers, but with primary teachers required to teach all subjects across the curriculum, it's unpractical.

"Primary sector principals are concerned that the new teacher qualification requirements are likely to result in poorer teaching quality rather than enhance it," he said.

"We are concerned that whilst it will take four years to become a teacher under the new scheme and teachers will all have a degree, the actual teacher training time will be significantly reduced and this in the end is what makes the difference for children."

Mr Drummond says classroom experience is a significant part of teacher training, "and much of it would be lost under this proposal".

The primary teachers union NZEI says it will fight any attempt to bring in performance pay.

"There are few places in the world where performance pay has made any difference to teacher quality," NZEI president Ian Leckie said.

"It's failed in many places ... good teaching has many aspects which aren't measured, it's hugely complex."

The government has also announced plans to increase student-teacher ratios, meaning bigger class sizes at most schools.