More expensive than what? A quick comment on CAP’s CSR report

The Center for American Progress today release a report on class size reduction authored by Matthew Chingos, who has conducted a handful of recent interesting studies on the topic.

This report reads more or less like a manifesto against class size reduction as a strategy for improving school quality and student outcomes. I’ll admit that I’m also probably not the biggest advocate for class size reduction as a single, core strategy for education reform, and that I do favor some balanced emphasis on teacher quality issues. I’m also not the naysayer that I once was regarding class size reduction and its relative costs.  There still exists too little decisive information regarding the cost-benefit tradeoffs between the two – teacher quantity and teacher quality.

I only had a chance to view this report briefly, and one specific section caught my eye – the section titled: CSR, The Most Expensive School Reform.

I found this interesting, because it included a bunch of back of the napkin estimates of the potential costs of CSR (based on reasonable assumptions), BUT PROVIDED NOT ONE SINGLE COMPARISON OF THE COST AND BENEFITS OF CSR TO ANY OTHER ALTERNATIVE.

You see – You can’t say something is the most expensive without actually comparing it to, uh, something else. That’s how cost comparisons work. Cost benefit analysis works this way too. You compare the costs of option A, and outcomes achieved under option A, to the costs of option B, and outcomes achieved under option B.

Implicit in this section of the report is that reducing class size for any given improvement in student outcomes is necessarily more expensive than improving student outcomes by the same amount by improving teacher quality.  In fact, explicit in the title of this section of the report is that pretty much any alternative that might get the same outcome is cheaper than CSR. That’s one freakin’ amazing stretch!

Here are a few quotes provided by Matt Chingos on this point:

A school that pays teachers $50,000 per year (roughly the national average) would save $833 per student in teacher salary costs alone by increasing class size from 15 to 20.30 The true savings, including facilities costs and teacher benefits, would be significantly larger. These resources could be used for other purposes. If all of the savings were used to raise teacher salaries, for example, the average teacher salary in this example would increase by $17,000 to $67,000.


The emerging consensus that teacher effectiveness is the single most important in-school determinant of student achievement suggests that teacher recruitment, retention, and compensation policies ought to rank high on the list.

Chingos goes on to address the various teacher effect and effectiveness based layoff simulations by authors including Eric Hanushek and how those simulations project larger gains than would be achieved by class size reduction. Chingos does acknowledge in the next paragraph that:

Teachers would need to be paid more to compensate them for the loss of job security. Providing bonuses to teachers in high-need subjects and schools would also consume resources. If these policies are more cost-effective than reducing class size, then increasing class size in order to pursue them would increase student achievement.

However, it would seem by the title and the rest of the content of this section that Chingos has jumped to a conclusion on this point. No actual cost comparison is made between improving student outcomes by improving teacher effectiveness versus improving student outcomes by class size reduction.

The relevant research question based on the hypothetical here is:

…on a given labor market with a given supply of teacher quantities and qualities, does the teacher that will teach for a salary of $67,000 with a class of 20 children get a better result than the teacher that will teach for a salary of $50,000 with a class of 15?

I’m not sure we know the answer to that, in part because the teacher labor market research also suggests that while there is sensitivity of teacher labor markets to salaries, it may take quite substantial salary increases to achieve comparable gains to class size reduction. Further, given class size and total student load as a working condition, the same teacher might teach a class of 15 for marginally lower salary than to teach a class of 20 (which could be the difference between a total load, at 6 sections per day, of 90 vs. 120 students, which is a pretty big difference).

I’ve been waiting for years for good answers to this tradeoff, and hoping for data that will provide better opportunities to address this question. Unfortunately, the wait continues.



  1. I think you’re going to have to wait even longer, Bruce, because how in the real world are you going to design an experiment or use existing data to test this question?

    Even if you separate teacher quality from salary, you have to control for all of the other variables: curriculum, SES, student characteristics, etc. Is this even possible? Are there two samples large enough that vary ONLY in class size?

    1. You are indeed correct… that estimating these tradeoffs will require a meticulously crafted experimental design. My only hope is that until we are able to conduct such an experiment, that pundits will cut the crap and stop making the argument that all other options are necessarily more cost effective than class size reduction. Sadly, I think they’ll continue on with these claims.

  2. 15 is a curious number to pick, because most public schools IME don’t deliberately choose to run with a number that low. Class size reduction in California is for 20 in K-3.

    I think, if you were doing the experiment, you could compare a situation of 25 students plus an aide, too.

    All this set aside, when I was a child, elementary classes of 35 were common… and it was definitely inferior to what my daughter experiences in a class of 20. So 20 feels pretty darn tiny to me.

    I also think that the assumption that someone who is a great teacher for 20 kids would automatically be a great teacher for 35 kids is incorrect. With a large head count, necessarily the teacher will have less time to give feedback and work individually with students.

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