John Hattie developed a way of ranking various influences in different meta-analyses according to their effect sizes. In his ground-breaking study ¿Visible Learning¿ he ranked those influences which are related to learning outcomes from very positive effects to very negative effects on student achievement. Hattie found that the average effect size of all the interventions he studied was 0.40. Therefore he decided to judge the success of influences relative to this `hinge point¿, in order to find an answer to the question ¿What works best in education?¿ Hattie studied six areas that contribute to learning: the student, the home, the school, the curricula, the teacher, and teaching and learning approaches. But Hattie did not merely provide a list of the relative effects of the different influences on student achievement. He also tells the story underlying the data. He found that the key to making a difference was making teaching and learning visible. He further explained this story in his book ¿Visible learning for teachers¿. Here is an overview of the Hattie effect size list that contains 138 influences and effect sizes across all areas related to student achievement. The list visualized here is related to Hattie (2009) Visible Learning. Hattie constantly updates this list with more meta studies. You can find an updated version in Hattie (2011) Visible Learning for Teachers.