Full Question: I am an instructional coach. Many of my colleagues and I have been working to stretch our thinking around assessment using your "Developing Assessment-Capable Visible Learners" resource. At this time, we are trying to accurately interpret your effect size data. For example, you suggest that teacher clarity with an effect size of 0.75 can be interpreted as nearly two years of growth in one school year. However, we are not confident that this is an accurate mathematical interpretation of your data. Are you able to clarify for us how to interpret an effect size of 0.75 in relation to student learning?
Answer: “Yes, we need to be careful about converting effect sizes to years' growth. A lot depends on how wide (creativity) or narrow (vocabulary) the task, and the ages of the students (in many domains like literacy the effects are much greater in elementary compared to high schools). The best is build local knowledge from your own data to set some estimates. Yes, 0.40 for a year and 0.80 for two years is the average--but there are so many flaws in the average and much care is needed here” (John Hattie, personal communication, April 9, 2019).