A study which assessed the impact of textbook provision in Kenya, like other input interventions, found no evidence that textbook provision increased average test scores, or that it reduced either grade repetition or dropout rates. However, textbooks benefited students with higher average test scores before the programme: those in the top 40% of the class before the programme increased their test scores between 0.14 and 0.22 standard deviations after one year, compared to a control group. This insight combined with several other studies helped illuminate a key reality common to many contexts: teachers teach to the top of the class – the few students who are at the level of the curriculum – while most students are left behind. Given the structure of education systems across many parts of the world, this is unsurprising. Many teachers are faced with classes with a wide variety of learning needs, dense and ambitious curricula, and high stakes primary leaving exams which incentivise teachers to move at the pace of the fastest learners.