Smaller class sizes might be good for some primary school children, but not all of them according to one expert.

Debate has been reignited after Simon Bridges announced a National government would reduce class sizes.

Massey University education expert John O'Neill told Mike Hosking in 2012, National's argument was one or two extra children in a classroom wouldn't make much of a difference.

He says back then they wanted to focus more on teacher quality.

'Bridges is not saying that teachers don't have enough time in the classroom and there is some evidence that if you have fewer children in the classroom then it does give teachers more time to work with children."

He says that there are other ways that could help teachers have more quality teaching time.

"One of the alternatives to reducing class size would be to reduce the amount of bureaucracy that teachers have to engage with and that is certainly one of the major complaints that you hear from teachers, it's not necessarily the number of children in the class although that is an issue, it's much more to do with their workload outside of teaching and the reality is that teachers spend much more time doing non-teaching activities during the course of their working week than they do actually teaching."

LISTEN ABOVE AS JOHN O'NEILL SPEAKS TO MIKE HOSKING