The Practical Tradeoff Between Class Size and Teacher Quality

My AFR oped today is on class size and teacher quality. Full text over the fold (with hyperlinks for anyone who wants more detail on the research).

In a Class of Their Own, Australian Financial Review, 14 July 2009

Few education policies are more popular than class size reductions. Alongside her faithful friend Laura Norder, Somala Classiz has appeared on the ballot in just about every state election over the past decade. And thus class sizes in Australia have steadily ratcheted downwards, gobbling up more money than any other educational reform.

The logic of class size reductions is easy to see. With fewer children in the room, teachers can spend more time with each student. Discipline challenges can be more easily managed, and lessons can be better tailored to the particular needs of the student.

Yet while smaller classes create the potential for better learning, there is no certainty that this potential will be realised. If teachers do not adapt their teaching style for a smaller group, there may be no improvement in performance. Indeed, it is even possible for a class size cut to reduce student performance. Smaller classes require hiring more teachers – and if the new hires are less effective than the incumbents, students could lose out.

In estimating the impact of class size on student performance, economists are naturally wary about drawing causal conclusions from the correlation between class size and student performance. If schools systematically stream gifted or struggling students into smaller classes, it will be difficult to know the true impact of class size on outcomes.

One way of solving this problem is to exploit class size rules, which grant schools an extra teacher when the number of students hits a given threshold. Across a number of developed countries, this approach suggests that once class sizes get below 30, students gain little benefit when another teacher joins the school and reduces class sizes.

Another research design is to randomly assign students into different sized classes, say by the toss of a coin. In the mid-1980s, Tennessee governor Lamar Alexander agreed with the state’s teachers to conduct a randomised class size experiment. If those in smaller classes did better, then class sizes would be reduced statewide. Although the experiment succeeded in showing that smaller classes raised test scores, some have worried about the incentives that Governor Alexander created. Can we be sure that the promise of across-the-board reductions didn’t influence how teachers behaved in the experiment?

In a new paper, Columbia University economist Jonah Rockoff brings some older evidence back into the debate, by reviewing the results of a series of randomised class size experiments conducted in the early-twentieth century. Prior to World War II, US education researchers conducted 24 randomised experiments to test the impact of class size reductions. In 22 of these experiments, there was either no difference in performance of children in large and small classes, or children in larger classes did better. Only two of the 24 experiments supported the notion that smaller classes improve student performance. Although these experiments might have had methodological shortcomings, they do suggest that modern policymakers should think twice before hitching their wagon to the class size horse.

Are there better policies than class size cuts? A growing body of evidence in the economics of education is pointing to the role of teacher quality as being paramount. And while salaries are not the only factor attracting skilled individuals into the teaching profession, higher pay does buy more effective teachers.

A rarely recognised fact is that if the education budget is not increased, smaller classes translate into pay cuts for teachers. In joint work with my ANU colleague Chris Ryan, we have tracked teacher pay since the mid-1980s. We find that relative to other university graduates (or relative to all employees), average teacher pay has fallen by about 10 percent. Over the same period, the student-teacher ratio (which closely tracks class size) fell by about 10 percent. The simple story of the past two decades is that teachers have bought class size reductions from their own wallets.

Put another way, new teachers in the 1980s were paid about a tenth more than the typical university graduate. Today, new teachers earn approximately the same as the typical university graduate. And as earnings inequality has opened up in the non-teaching sector, the uniform salary schedule in teaching looks increasingly unattractive to talented youngsters. It is therefore hardly surprising that the average academic aptitude of new teachers has also declined.

So next time you hear Australian politicians spruiking smaller classes, ask why they’ve never been willing to put their rhetoric to the test with a randomised evaluation of smaller classes. Better-paid teachers doesn’t look so good on a manifesto, but it might just have a bigger impact in the classroom.

Andrew Leigh is an economist in the Research School of Social Sciences at the Australian National University.

I was tempted to point out that if the current trends persist, we’ll eventually end up with minimum-wage teachers running classes of a dozen students.

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5 Responses to The Practical Tradeoff Between Class Size and Teacher Quality

  1. Kevin Cox says:

    If the decrease in class size brings about a decrease in salaries then we could reasonably expect the reverse – an increase in class size bringing about an increase in salary. This would be news to lecturers in the Universities where the opposite seems to be the case. The increase in class sizes has been accompanied by a decrease in salaries.

    I also expect that for some children the decrease in class sizes does not matter but others it will matter. This is always to problem with “rules” of one size fits all. It is almost certainly better to leave schools to decide how they divide up the money they receive.

  2. conrad says:

    I think there are three often over-looked factors:
    (1) the effect on students who are outliers but don’t change means much.
    (2) the effect on retaining teachers (do large classes cause teachers to change careers faster or would more money compensate for this?)
    (3) If I was a teacher, I wouldn’t buy your argument since governments don’t necessarily allocate education money rationally — it tends to be public perception driven. Thus reducing class sizes is probably a win-win situation for teachers (and of a course, what has been a loss-loss for universities) — few people wants to see classes of children of any size in abysmal situations.
    Personally, looking at the university system where classes have got larger and larger and students now learn less and less from more and more jaded people, it seems to me there is also a lot of long term stuff going on that looking at a single time-slice won’t tell you.

  3. Alice says:

    “””This would be news to lecturers in the Universities where the opposite seems to be the case”””.

    I may not mind larger class sizes if I had been compensated for more noise, less time for one on one interaction and a larger share of marking which, of course, has diminshed the marginal rate of my pay as more time is now spent on activities at a lower rate of pay….( admin, marking, and communications and recording). I am a casual academic who has taught thousands of first year undergrad econ students sibce 1996…I am now part of Taylors production line…I have friends who used to do this job also and greatly enjoyed it. But I have watched my class sizes grow from 23-25 to 35-40 in this job over 14 years, but now tutors are walking away (even first year grads who unis now rely on to teach these large volume subjects dont last longer than 6 months or a year – so much for experience in teaching)….

    There comes a tipping point at which the search for further efficiencies by university managements of teaching of students at the coalface in unis actually results in the growth of other unanticipated (clearly … but somehwat disconcertingly) inefficiencies.

    I have received comments for the past few years in my SFS….”too many in the class to get help”…so do I get negatively surveyed by students who feel this way, over a situation I have no control over?


  4. MsLaurie says:

    Anecdata to be sure, but my mother and aunt, both teachers of many years experience, will swear that smaller class sizes are better than a pay rise.

    Its not so much the interaction with the kids – although they both say that the larger the class size the easier it is for kids to get ‘missed’ – its the marking and administrivia of additional students which eats into their time.

    Things like writing reports for each child, marking each maths test, spelling test, reviewing each project. Each additional child is a lot of extra work, and there are no economies of scale. And most of that additional work is done on weekends or after hours. A 10% pay rise won’t get you back your Saturday, but twenty kids compared to thirty probably will.

  5. Patrick says:

    Thanks MsLaurie, I had never thought of it that way – in effect, a class size cut is a reduction in working hours. No wonder teachers are so in favour of class size cuts!!

    But as for economies of scale, well, you only have to prepare one set of class materials, prepare one class-room, clean up one class-room once, … there are certainly economies of scale just not necessarily in marking and the aspects of administrivia you were thinking of.

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