The Australian Education Union today begins another campaign to bring class sizes down to 20. As Justin Wolfers and I argued in 2002, in response to a surprising similar "twenty is plenty" campaign, the Bracks Government (which seems to be the main target) would do well to ignore the campaign. The econometric evidence on class size suggests that once classes get below 30, the benefits to students of further class size cuts is small or zero.
Teachers may also wonder whether such a campaign serves their best interests. I’ve been working quite a bit this month on teacher pay and teacher aptitude, and am increasingly coming to the view that declining teacher pay, relative to similar occupations, is a big reason why the aptitude of new teachers has fallen (for evidence on this point, watch this space).
Why has relative teacher pay fallen? One possibility is that cutting class sizes chewed up a lot of the education budget. After all, a 10% class size cut costs the budget as much as a 10% salary increase. The graph on the left shows the relationship between the two. Of course, correlation doesn’t imply causation, but given the trends of the past quarter-century, I’m surprised the AEU is still pushing smaller classes.