What does the evidence say about the impact of K-12 class size?
March 5, 2014 2:09 PM   Subscribe

What does current research say about the impact of class-size in K-12 education? My town is debating how to address a 35% increase in the school-age population. How much do we raise taxes and do we let class sizes increase? Lots of people are throwing around anecdotes about their own experiences. I'd like to know what the people who study this have to say.

Some details about our school system are probably important:
  • Our town has a long tradition of having excellent schools.
  • We have several neighborhood-based K-8 schools and one high school. We do not have any magnet schools, exam schools, or middle schools.
  • Classrooms are inclusive, with special-needs kids taught alongside typically developed kids.
  • The school system doesn't use tracking to segregate high-performing kids. They are attempting to use in-class differentiation to keep the brightest kids engaged and performing at their potential.
  • A few years ago average class size was around 18. Currently it's up to 21. Options range from bringing it back to 18, letting it go up to 23/24, or keeping it where it is.
I am a parent with two kids in the school system. I am hoping to find arguments in favor of smaller class sizes, but ultimately I really want to know what the research says. Also, I'm sick of people talking about how they did fine 40 years ago in classes with 30 kids, ignoring the fact that they weren't in inclusive classrooms, didn't have to deal with No Child Left Behind or frequent standardized tests, etc etc.
posted by alms to Education (7 answers total) 6 users marked this as a favorite
This looks like a pretty helpful research summary. Among the points it makes is that instead of comparing smaller/larger class size as the only options, perhaps the better approach is comparing several different approaches to dealing with the students, comparing the cost and effectiveness of all the various solutions, and investing money in the way that makes the most sense--perhaps a combination of class size and other efforts to improve student outcomes--in terms of overall student results, not just class size per se. Quoting:
When school finances are limited, the cost-benefit test any educational policy must pass is not “Does this policy have any positive effect?” but rather “Is this policy the most productive use of these educational dollars?” Assuming even the largest class-size effects, such as the STAR results, class-size mandates must still be considered in the context of alternative uses of tax dollars for education. There is no research from the U.S. that directly compares CSR to specific alternative investments, but one careful analysis of several educational interventions found CSR to be the least cost effective of those studied.

The popularity of class-size reduction may make it difficult for policymakers to increase class size across the board in order to sustain other investments in education during a period of budget reductions. In that context, state policymakers should consider targeting CSR at students who have been shown to benefit the most: disadvantaged students in the early grades, or providing a certain amount of funding for CSR but leaving it up to local school leaders on how to distribute it.
posted by flug at 2:25 PM on March 5, 2014 [1 favorite]

Here's something:
Class size, together with students’ instruction time, teachers’ teaching time and teachers’ salaries, is one of the key variables that policy makers use to control spending on education. Between 2000 and 2009, many countries invested additional resources to decrease class size; however, student performance has improved in only a few of them.

Apart from optimising public resources, reducing class size to increase student achievement is an approach that has been tried, debated, and analysed for several decades. Some countries like Finland favour smaller class sizes (20 students of fewer) and are among the most successful countries in the PISA study. However, other countries like Korea have much bigger classes (34 students and over) but also feature at the top of the PISA ranking. What other variables than class size may explain the success of countries like Korea?

Findings from the OECD Programme for International Student Assessment (PISA) suggest that systems prioritising higher teacher salaries over smaller classes tend to perform better, which confirms research showing that raising teacher quality is a more effective measure to improve student outcomes.
Perhaps you could increase class sizes and increase taxes, so you can pay teachers 25% more than currently is the case...
posted by jsturgill at 2:41 PM on March 5, 2014

Class size matters considerably more in the early grades (pre-K through 2, say). It also matters a lot more for children in poverty than for children who are middle class. Here's a Brookings analysis with links to a lot of research.

In my practical experience, one thing that gets left out of the discussion a lot with high school class size is that different subjects might have different class-size needs. For example, if you have 20 students per class now across all subjects, it might be desirable to let math classes float up to 24 students if it meant you could bring lab sciences down to 16. If your school splits literature and writing into two separate courses, maybe you'd be willing to have larger literature classes so you could have smaller writing classes, where the teacher's grading load is far more intensive.

I would definitely have this conversation with teachers and administrators in your district, and ask them how they would target class size/extra staff people. Sometimes you ask them, "We can hire another second grade teacher and shrink your classes by four students each," and the teachers are like, "We don't want smaller classes, we want a reading interventionist." We asked our middle schools and they wanted dedicated counselors. You have lots of experts right there in your district who have to go to tons of continuing ed on this sort of thing and have lots of ideas about what they'd do with an extra $50,000. :)
posted by Eyebrows McGee at 2:44 PM on March 5, 2014 [4 favorites]

Thank you for the responses. I'd like to reiterate that the question is about the impact of class size. If data exists that is specific to inclusive classrooms in the US that would be ideal.

My question is not, "what is the best way maximize educational outcomes given limited financial resources". That's an interesting broader question but it's not the question I'm asking here.
posted by alms at 2:49 PM on March 5, 2014

Thank you for the responses. I'd like to reiterate that the question is about the impact of class size. If data exists that is specific to inclusive classrooms in the US that would be ideal.

The impact of smaller class sizes is positive (it's almost always a good or neutral thing), variable (not guaranteed & incosistent), and relatively tiny (when present). As three people have said in different ways. The other two links given are to the same page, which is more on target than my link. They address results of smaller class sizes in the US directly:
Studies of class size in Texas and Israel also found benefits of smaller classes, although the gains associated with smaller classes were smaller in magnitude than those in the Tennessee STAR study. Other rigorous studies have found mixed effects in California and in other countries, and no effects in Florida and Connecticut.

Because the pool of credible studies is small and the individual studies differ in the setting, method, grades, and magnitude of class size variation that is studied, conclusions have to be tentative. But it appears that very large class-size reductions, on the order of magnitude of 7-10 fewer students per class, can have significant long-term effects on student achievement and other meaningful outcomes. These effects seem to be largest when introduced in the earliest grades, and for students from less advantaged family backgrounds.


Class-size reduction has been shown to work for some students in some grades in some states and countries, but its impact has been found to be mixed or not discernable in other settings and circumstances that seem similar. It is very expensive. The costs and benefits of class-size mandates need to be carefully weighed against all of the alternatives when difficult decisions must be made.
posted by jsturgill at 3:45 PM on March 5, 2014

Google will show you a fair amount of evidence that smaller classes are better, but it's not quite as simple as that. Teacher training, teacher effectiveness, amount of students at risk, levels of disabilities within the class, school resources in general...all of these things are factors.

An interesting opinionator from the NYT discusses the issue and has some links.

I wish there were a simple answer to this. I run a school where we have no more than 8 students to 1 teacher, and our kids all have severe emotional disabilities, and not a whole lot of teaching goes on some days.

I've worked in systems with 30 neurotypical, high-achieving kids with 1 teacher and a lot of learning happened.

Bear in mind this is a very difficult thing to quantify because so many factors determine what makes a school system "good:" test scores, class size, teacher salary, Title IX money, etc. You can't just say, "Smaller class size is better," because you can't isolate ONLY class size from many other inequal factors.
posted by kinetic at 4:27 PM on March 5, 2014

You'll get plenty of data about class size, smaller is better.

One thing you may have an issue with is actual buildings to house the classes. I will propose that if your school district goes to a Year Round Schedule, that you can have 1/3 as many students in the same building.

The school I went to had 9 weeks on/3 weeks off schedule and it was fantastic! The schedules stagger, and classrooms change around, and it's a great way to keep staff in the school employed year round.

So, that is a money saving answer to one part of the question. You'll still need to employ more instructors, but you would have needed to do that anyway.
posted by Ruthless Bunny at 6:38 AM on March 6, 2014

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