Why is class size reduction's effect size so modest?

Hattie's analysis shows class size reduction (d = 0.21) is below his ‘hinge point’ of 0.40 for meaningful educational impact. Research suggests teachers rarely change their instructional approach when class size decreases, limiting the benefit. Changing pedagogy amplifies class size benefits significantly.

What interventions have the highest effect sizes in education?

From Hattie's Visible Learning synthesis: collective teacher efficacy (d = 1.57), self-reported grades/expectations (d = 1.33), Piagetian programmes (d = 1.28), response to intervention (d = 1.09), metacognitive strategies (d = 0.60), and classroom discussion (d = 0.82).

Class Size Effect Size Calculator (Hattie Visible Learning)

Formula Definitions

The Class Size Effect Size Calculator (Hattie Visible Learning) works by applying a well-defined formula to the values you enter. Understanding the formula behind the calculation helps you interpret the result and check that your inputs are correct. Below we break down the key components that drive the Class Size Effect.

The core formula used by this calculator is:

Result = f(inputs, settings)

Each variable in the formula has a specific meaning:

inputs — Values entered into the Class Size Effect.
settings — Options, units, or parameters that adjust how the calculation is performed.
Result — Computed output for the chosen inputs and settings.

How to Use This Calculator

Enter the required values. Enter the required values into the Class Size Effect Size Calculator (Hattie Visible Learning) input fields.
Adjust settings. Adjust any settings, select applicable options, or choose units as needed.
Calculate the result. Press Calculate to compute the result using the underlying formula.
Interpret the output. Review and interpret your result using the provided context, reference ranges, or explanatory notes.

Glossary and Definitions

Input: A value entered into the calculator to be processed.
Output: The computed result returned by the calculator for the given inputs.
Setting: An option that adjusts how the calculation is performed, such as unit selection or mode.
Class size effect: A key concept referenced by the Class Size Effect: Estimate Cohen's d effect size of class size reduction on student achievement using Hattie's Visible Learning synthesis data. Hattie's meta-analysis reports d = 0.21 for class size, below the 0.40 'hinge point' of meaningful educational interventions.
Hattie d: A key concept referenced by the Class Size Effect: Estimate Cohen's d effect size of class size reduction on student achievement using Hattie's Visible Learning synthesis data. Hattie's meta-analysis reports d = 0.21 for class size, below the 0.40 'hinge point' of meaningful educational interventions.
Visible Learning: A key concept referenced by the Class Size Effect: Estimate Cohen's d effect size of class size reduction on student achievement using Hattie's Visible Learning synthesis data. Hattie's meta-analysis reports d = 0.21 for class size, below the 0.40 'hinge point' of meaningful educational interventions.
Cohen d education: A key concept referenced by the Class Size Effect: Estimate Cohen's d effect size of class size reduction on student achievement using Hattie's Visible Learning synthesis data. Hattie's meta-analysis reports d = 0.21 for class size, below the 0.40 'hinge point' of meaningful educational interventions.
Class size reduction: A key concept referenced by the Class Size Effect: Estimate Cohen's d effect size of class size reduction on student achievement using Hattie's Visible Learning synthesis data. Hattie's meta-analysis reports d = 0.21 for class size, below the 0.40 'hinge point' of meaningful educational interventions.
Effect size education: A key concept referenced by the Class Size Effect: Estimate Cohen's d effect size of class size reduction on student achievement using Hattie's Visible Learning synthesis data. Hattie's meta-analysis reports d = 0.21 for class size, below the 0.40 'hinge point' of meaningful educational interventions.