Old Hat(tie)? Some things you ought to know about effect sizes
Ever since Hattie published Visible Learning back in 2009 the Effect Size has been king. For those of you who don't know, an effect size is a mechanism for comparing the relative merits of different interventions. Hattie pointed out that everything that a teacher does will have some effect but that there will also be an opportunity cost: if you're investing in time in one type of intervention you will be neglecting other types of intervention which might have a greater impact. He therefore used effect sizes to try to establish what has the greatest influence on student learning so that we [...]