The students of a very bad teacher will learn, on average, half a year’s worth of material in 1 school year. The students in the class of a very good teacher will learn a one-and-a-half year’s worth of material. That difference amounts to a year’s worth of learning in a single year. Teacher effects dwarf school effects: your child is actually better off in a bad school with an excellent teacher than in an excellent school with a bad teacher. If you rank the countries of the world in terms of the academic performance of their schoolchildren, many countries could climb the ladder simply by replacing the bottom 6-10% of public-school teachers with teachers of average quality (Jack Welch tells us to do this in our companies every year). After years of worrying about issues like school funding levels, class size, and curriculum design, many reformers have come to the conclusion that nothing matters more than finding people with potential to be great teachers. Summarised from Malcolm Gladwell’s excellent new book ‘What the Dog Saw.’