Has John Hattie really found the holy grail of research on teaching? An extended review ofVisible Learning

In this article the author reviews and discusses John Hattie’s book Visible Learning. In this book Hattie presents the results of a meta‐meta‐analysis on the conditions of successful teaching and learning in schools. Hattie’s work is based on more than 800 meta‐analyses, and these meta‐analyses are substantiated by more than 50 000 empirical research studies. Among the six groups of factors influencing successful learning in schools—student, home, school, teacher, curricula, teaching—the factor ‘teacher’ seems to have the strongest effect. Hattie not only evaluates empirical research but also places the results in a theoretical context of a theory of teaching and a certain concept of teacher professionalism. The author discusses Hattie’s approach to combine empirical research and conceptual work on teaching and on teachers’ work. The limits of meta‐analyses and future meta‐meta‐analyses are pointed out.