Tuesday, November 30, 2010

Education cuts, the National Plan and class sizes

Because of the dire fiscal situation, it seems some cut-backs to educational spending would be inevitable. The National Plan is pretty vague on education (amongst other things). Discussing the plan in the Irish Times Colm McCarthy remarked “The plan reflects successful lobbying to exempt the education budget from severe cuts. This is being justified in terms of the importance of holding with existing targets for pupil-teacher ratios, notwithstanding the dearth of evidence that reducing these ratios weakens educational outcomes in any measurable way.”

Is this really true? Well no. Few parameters in the economics of education have been so well studied as the effect of class size on educational outcomes. There are dozens and dozens of studies. So what’s the answer then? Well this is where it gets complicated. Firstly, we have no good evidence for Ireland that I am aware of. If this is what Colm McCarthy means then he is correct but then we don’t have any evidence on lots of things for Ireland and absence of evidence is not evidence of absence. What does the international evidence say then? The first complication is that one should not expect one answer. Primary schools are different from secondary schools, a class of 40 is different from one of 20 and Korea is not Bangladesh so variation in measured effects is to be expected. A further problem, which non academics may not care about but is important, is that methods for estimating these effects vary widely and this partly explains some of the variation.

The most well studied country is the US. The STAR experiment in Tennessee is generally considered a well designed study and points to significant benefits from smaller classes but in that case the reductions were big (around 9 pupils on average). A “natural experiment” in Connecticut came up with a “precisely estimated zero” effect (Hoxby). The famous Maimonides Rule study for Israel (Angrist & Lavy) found positive effects of smaller classes but similar work for the Netherlands found the opposite (papers by Levin, Dobbelstein et al). A cross country study using TIMSS data (Woessman & West) found a mixed bag of results. Some reviews of the evidence point to negligible effects over all (see the work by Eric Hanushek) while other meta-analyses point to clear benefits from reducing classes. So rather than a dearth of evidence there is too much of it or at least there is not enough consensus and you can pick a study to suit your prejudice (or “prior” to give it its scientific name).

What’s striking about this literature is its near obsession with one variable, class size. Other measures of quality are almost entirely ignored. Ask yourself or someone else was their school good and they will quickly you reasons why it was or wasn’t. Class size tends not to be prominent a reason in my experience. This isn’t scientific but it does remind us that lots of things, some hard to measure, go into making a good school. One factor that everyone mentions is their teachers. Curiously, measuring the quality of teachers and the effect it has on outcomes does not feature much in the policy debates.

In the absence of clear evidence it probably makes sense that any damage from increased class effects is minimized by favouring more socially disadvantaged schools and those schools with the biggest class sizes.


David Madden said...

Good post, Kevin, even though vested interests will persist in looking for definitive evidence one way or the other in what is a complex issue. One thing that strikes me is that there is a lot of within-school variation in class sizes, depending upon the size of the cohort intake and also attrition as kids leave the school for whatever reason. Has this variation ever been exploited to invesutigate the effect of class size, given that you would have control over school fixed effects?
Another point that strikes me (arising from my observations as a Parent Association rep) is that if a school does lose teaching resources and faces an increase in class size, the increase does not fall uniformly on all classes. A good school principal may well be able to offset the effects of larger class sizes simply by assigning her best or better teachers to those classes. And as you say, teacher quality is likely to have a far greater impact upon student outcomes than class size.

Kevin Denny said...

Ah you need to come to my class today to get the answer! But since... So most of the literature deals with between-school sorting by fixed effects like you say so its generally about within-school, certainly the papers I cited. The teacher selection could well play a part but I think thats a bit of a black hole in the literature:we don't measure it so we don't model it.
The measures that are available are things like experience, qualifications. Fair enough, but think of your good and bad teachers: is that what made the difference?
Hanushek and others have been emphasizing that its teacher quality that matters.

Martin Ryan said...

For what it's worth (and it's probably worth something given it's the position of the man running one of the world's biggest philanthropy initiatives), Bill Gates has urged "an end to efforts to reduce class sizes. Instead, he suggests rewarding the most effective teachers with higher pay for taking on larger classes or teaching in needy schools."

The quote is from a recent article in the New York Times:

Gates Urges School Budget Overhauls