Class sizes according to Professor Hattie

Many have been going on about class sizes recently – mainly due to the fact that Labour have released their education policy and the mainstream media and far right bloggers of this world have decided they are planning to spend all their money on reducing class sizes. No mention of the fact that Labour’s policy is a comprehensive package that actually lists a few more things than just class sizes.

Since Farrar is harping on about class sizes having no effect on learning outcomes or student achievement or whatever he calls it, I thought I’d actually do a bit of research. After a bit of interweb digging I found a 1999 paper from Professor Hattie outlining the findings of his decade-long meta-research into the influences on student learning.

You can read it all if you like, or you can scroll down to the section on class sizes, or you can just read the bit I cut and pasted below.

The research on the effects of class size has been among the more voluminous in educational research with very systematic findings:

  • Achievement, attitude, teacher morale, student satisfaction gains are appreciable in smaller classes, so long as we recognise that small classes mean 10-15, as there are negligible gains between 40 to 20 students per class.
  • This effect was the same for primary and secondary schools, across all subjects, and across various ability levels.
  • There is little evidence that instruction methods change when class size is reduced, although a large part of improvement can be explained by improvements in student task engagement.

Reducing class sizes from the 30’s to the 20’s is in the right direction, but there is little support for the claim that there are increases in student achievement or satisfaction, or teacher attitude or morale. Only when the class size reduces to 15 or below are there appreciable positive benefits.

(Hattie, 1999)

So you can see Professor Hattie is saying that there are negligible gains when class sizes are between 20 and 40, but there is an effect seen when class sizes reach the small size of 10 – 15 he is referring to (I would imagine that is roughly about the size of classes at some of those private schools National & ACT politicians like to segregate their children within – away from the prying eyes of the rest of us po’).

Being a teacher of a fairly small class (24 this year) compared with the norm, I am acutely aware of the impact not teaching 31 kids has on both my time and my teaching. It’s great having a small class. I remember back in term one when there was some kind of stomach flu going around AND we had a sports tournament on the same day. That day I fell within that magical range of 10 – 15. Man it was sweet. Unfortunately it was only one afternoon so I doubt whether I was able to have any discernible impact on their learning. The other kids were back from the sports day before I could. I just had to make do with getting it done over the rest of the year.

Of course, I’m being facetious, but there is some truth in what I say. The smaller my class is, the easier it is for me to teach. I can get around more students during a session. You ask any teacher. Smaller class sizes make it easier for us to do our jobs. If it’s easier for us to do our jobs, then that is going to impact on outcomes for our students. Simple.

Another important point to make is this: Professor Hattie’s research looked at over 100 effects on student learning. His meta-analysis took over 10 years to do and compiled research that included over 50 million students. There are thousands and thousands of effects on their learning. I would argue that you cannot take any of these effects out of context. Whatever effect you are looking at – teacher instruction, class environment, teacher style, instruction, homework, home life, parent involvement, peer influence – they are all intertwined. All of the hundred or so effects Professor Hattie listed are linked. You can’t just pluck out ‘class size’ or ‘teacher instruction’ to make your case because ‘home life’ and ‘peer influence’ are going to make their mark at the same time.

So media and Farrar, if you’re going to quote research, actually do your research rather than quoting a list of “effects” and pointing to class size down at number one hundred and something and saying, “Look! Class sizes have no effect on student learning so Labour is dumb.”

Mr B


INFLUENCES ON STUDENT LEARNING – John Hattie, August 2, 1999.


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