Reading 4 (Extension): Reading Between the Lines

DOES CLASS SIZE MATTER?

Legislators are spending billions to reduce class sizes. Will the results be worth the expense?

By Ronald G. Ehrenberg and Dominic J. Brewer. (updated)

In many countries, including Australia, the United States and Canada, governments continue to invest heavily in class size reduction initiatives. In Australia, national data show that the average student to teacher ratio fell to 12.9:1 in 2024, continuing a long‑term downward trend. State level datasets from New South Wales and Victoria confirm similar patterns, with primary class sizes gradually declining through 2024 - 2025. These investments reflect a widespread belief that smaller classes lead to better learning outcomes, particularly in the early years of schooling.

Hundreds of studies have examined whether smaller classes improve academic performance. While early research produced mixed results, many recent analyses show modest but meaningful benefits, especially for disadvantaged or academically at-risk students who are at greater risk of falling behind or eventually choosing to drop out. The most influential evidence remains the Tennessee Project STAR experiment, which randomly assigned students to different class sizes. Its findings demonstrated that students in smaller classes performed better academically, and later research linked these early advantages to higher rates of educational attainment, college participation and other positive adult outcomes, although evidence for direct effects on adult earnings is more mixed.

Education continues to be a pillar of modern society and one of the strongest predictors of long-term wellbeing, influencing intellectual, social and economic outcomes. International comparisons, such as PISA, have intensified debates in countries like Australia, where policymakers closely monitor performance across different age brackets, for example the four to seven age bracket and relative to other OECD nations. Although class size is often highlighted in these discussions, contemporary research emphasises that achievement differences are also shaped by teacher quality, curriculum design and broader system structures.

Of all the proposed reforms, reducing class size remains one of the most publicly appealing. It is easy to understand, politically attractive and strongly supported by parents and teachers. However, class-size reduction is also expensive. Hiring additional teachers and expanding classroom space represent significant costs, and recent evaluations suggest that improving teacher quality or targeting specific student groups may accomplish more than universal reductions. Its uncomplicated appeal is one reason for its popularity, although the costs can dwarf those of many alternative reforms. Governments have committed substantial resources to these initiatives.

The renewed surge of interest in smaller classes has prompted further analysis of Project STAR and similar initiatives. These studies generally confirm that small classes can improve achievement, particularly in the early years, but the magnitude of the effect is moderate and varies across contexts.

Why do Teachers Prefer Small Classes?

EDUCATORS HAVE a multitude of explanations for why smaller classes might be expected to improve academic performance. Much of the support for smaller classes comes from anecdotal evidence. Fewer students in a classroom can mean less noise and disruptive behavior, which may give the teacher more time for instruction and more freedom to engage students in varied activities.

Smaller classes also allow teachers to encourage more discussion, assign more writing and closely examine students' work. However, evidence indicates that teachers do not always substantially change their instructional practices in smaller classes, which may limit the potential gains. Smaller classes may also help improve student self-esteem.

Ingredient X: A Teacher’s Adaptability

The conventional wisdom about small classes is that they minimize disruption and allow more individual attention. However, many studies find that teachers do not always substantially adjust their instructional practices in smaller classes to match the size of their class.

If teachers work in more or less the same way regardless of class size, one explanation for the benefits observed in studies is that teachers whose methods are naturally suited to smaller classes tend to perform especially well when given such environments. Teachers who successfully adapt to smaller learning environments may be able to accomplish more ambitious learning goals.

This interpretation is consistent with findings that performance gains from small classes are generally strongest in the early elementary grades, with less consistent evidence of additional academic gains from later reductions in class size. The strongest effects are often seen among struggling students and underachievers.

What the Record Shows

Researchers have attempted to analyse the effects of class size by reviewing large-scale data. Over recent decades, student to teacher ratios have declined in many countries, including Australia. However, changes in academic performance cannot be attributed to class size alone. Numerous factors, such as family background, school resources, demographic shifts and teacher quality, influence outcomes. As a result, researchers increasingly rely on controlled studies rather than simple correlations to understand the true impact of class size. A myriad of influences, including demographic shifts, makes interpretation difficult.

How Reliable are the Findings?

Do these findings mean that class size makes no difference? Not necessarily. Not all improvements translate into higher retention rates or earnings later in life.

Another reason for caution is that it remains difficult to isolate the effects of class size from the many factors that influence student performance, including family background, school resources and teacher quality. Only a fraction of observed differences can be confidently attributed to class size alone, especially in poorly designed studies.

Researchers now rely more on controlled studies than on simple correlations. Demographic changes and enrolment growth, with 45,008 additional students enrolled nationally in Australia in 2024, make it difficult to isolate class-size effects.

The bottom line is that well-designed studies generally find that smaller classes benefit students, particularly in the early grades and among those at risk of underachievement, although the overall effect size is moderate and sometimes negligible when compared relative to other interventions.

Project STAR

The notable exception remains the STAR project, in which students were randomly assigned to different class sizes. It showed that students in smaller classes performed better, especially in early grades.

Some analysts found that the benefits of small classes appeared early and could persist into later schooling, while more recent research suggests these early advantages may also be linked to longer-term outcomes such as higher educational attainment and earnings.

Other researchers argue that it is difficult to separate the long-term effects of class size from other influences, such as family background and later schooling experiences.

Even so, the STAR findings continue to support the conclusion that smaller classes provide a statistically significant benefit.

Two Views: California and Wisconsin

The challenge for legislators is to develop sensible policies based on research. Large-scale programs such as California’s initiative illustrate the difficulties of rapid implementation.

Such programs can increase demand for teachers, sometimes leading to shortages of qualified staff, particularly in disadvantaged areas.

While U.S. programs like California’s and Wisconsin’s SAGE provide mixed but informative results, Australian policymakers face similar challenges: teacher shortages, uneven distribution of qualified staff, and rising enrolments in some states (e.g., South Australia and Western Australia at 2.2% growth in 2024)

Evidence from these initiatives suggests small but measurable improvements in student achievement, although the gains are generally not large.

More targeted programs, such as Wisconsin’s SAGE, which focused on disadvantaged schools and struggling students, have shown stronger and more consistent results.

What are the Implications?

Studies such as STAR and SAGE make it difficult to argue that reducing class sizes makes no difference, particularly in early education.

At the same time, a large body of research now indicates that teacher quality has a greater impact on student performance than class size alone.

Legislators and administrators need more solid information on the relative costs of different strategies. Current evidence suggests that targeted class-size reduction, combined with improvements in teacher quality and instructional practices, is likely to be more effective than across-the-board reductions.

Adapted from Ehrenberg & Brewer, “Does Class Size Matter?”