Understanding Effect Size in John Hattie's Research

By Melissa Benitez, The Teacher Tutor

June 12, 2024

In his seminal work "Visible Learning," John Hattie uses the concept of effect size to measure the impact of various educational strategies on student learning outcomes.  Effect size is a statistical metric that quantifies the strength of the relationship between two variables.  In the context of education, it helps to determine how much a particular strategy influences student achievement. 

definition of effect size

Effect size is a standardized measure that indicates the magnitude of a strategy's impact.  It is typically expressed as a decimal.  In Hattie's framework, the effect size is used to compare the effectiveness of different teaching methods, strategies, and interventions. 

interpretation of effect size

Hattie interprets effect size using the following scale:

• 0.00 - 0.15: Negligible Effect

• 0.15 - 0.40: Small Effect

• 0.40 - 0.60: Moderate Effect

• 0.60 and Above: Large Effect

In educational research, an effect size of 0.40 is considered the "hinge point" or the average impact of all interventions.  Interventions with effect sizes above 0.40 are seen as having a greater than average impact on student learning. 

examples of effect sizes

1. Feedback (Effect Size: 0.70): Feedback is one of the most powerful influences on student achievement, with an effect size of 0.70.  This means that effective feedback can significantly enhance student learning outcomes, making it more impactful than many other strategies. 

2. Teacher-Student Relationships (Effect Size: 0.72): Positive teacher-student relationships have a very high effect size of 0.72.  This highlights the importance of fostering a supportive and trusting classroom environment to boost student performance.

3. Repeated Reading (Effect Size: 0.75): Repeated reading interventions have an effect size of 0.75.  This indicates a substantial positive impact on students' reading comprehension, particularly benefiting struggling readers. 

4. Class Size Reduction (Effect Size: 0.21): Reducing class size has an effect size of 0.21, which falls into the lower effect range.  While often advocated for, it is less impactful compared to other interventions like feedback or teacher-student relationships. 

application of effect size

Hattie's use of effect size allows educators to prioritize teaching strategies that have the most significant impact on student learning.  By focusing on strategies with higher effect sizes, schools and teachers can implement practices that are more likely to yield substantial improvements in educational outcomes. 

conclusion

John Hattie's concept of effect size provides a clear and quantifiable way to assess the effectiveness of educational interventions.  By understanding and utilizing effect sizes, educators can make informed decisions about which strategies to adopt in order to maximize student learning. 

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