Class sizes and teacher effectiveness

I was reading about teacher effectiveness and how it’s the most crucial factor in achieving good student outcomes.

It was alleged that the most important thing in the mix — the mix being all the possible factors that contribute to student performance — are excellent teachers. The example was that of the Californian experiment when the State decided to implement a policy of class size reduction (CSR) as a quick and magic fix for poor quality student outcomes, especially in poorer areas (Imazeki, 2003)

To quickly fill all these new classes, less qualified, and less experienced teachers were hired. The overall effect was that the results were either bad or good. I can find several papers in the academic literature that say it was worse as teacher quality was the greater factor and only one paper from a think tank that said CSR was more important. (, 2012)

So. There you are. My initial reaction is that there is a pressure group out there denying academic study. But I have not had time to read them in depth. What I am really doing is parking this subject here with some sources to come back to later if and when required. I will have to go through this more thoroughly.

Smaller isn’t always better

I did find this pithy summary of the effect of class sizes. It certainly made me sit up when it said that class sizes of less than 10 “lacks energy”. This was my experience with small class numbers in Spain.

“Teachers know that, when it comes to class size, certain thresholds matter. A class with fewer than 10 students lacks energy, and is hardly worth teaching. Seminars — where each student has a chance to participate, share their ideas and thoughts with the rest of the class — work well with up to 15 or 20 students. Above 20 students, it becomes necessary to lecture, but it is still possible to have some group work, and get to know each student individually. With more than 40 students, it is impossible to do anything but lecture.

In lecture-style classes, student numbers are relatively unimportant. A class of 60 is little different from a class of 120. Large classes — 300, 400, 1000 students — can be impersonal, and students tend to sit in the back and whisper. But given a choice between being one of 300 students listening to an engaging and entertaining speaker, or one of 100 students listening to a dull and pedantic one, most students will pick the good talker every time.

This has been known for centuries. Maimonides formulated a rule almost a thousand years ago: when a class has 40 students, it is necessary to hire a second teacher. (Universities today use a similar rule, hiring teaching assistants for classes with much more than 40 students.)” (Woolley, 2011)

Sources (2012) In California, class size reduction led to significant improvements in student achievement, parental involvement, and teacher retention.

Imazeki, Jennifer (2003) Class-size Reduction and Teacher Quality: Evidence from California. IN School Finance and Teacher Quality: Exploring the Connections

Woolley, Frances (2011) University class sizes: Smaller isn’t always better  The Globe and Mail. 4 Nov 2011

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