It’s not controversial to note that materials used in language classrooms need to tick a lot of boxes. They need to be engaging, but not be so long and complex that they out-live their potential to engage; they need to be pitched at a level which is challenging, but not so challenging as to risk inviting failure; they need to convince learners as well as teachers that within them reside useful language learning opportunities in vocabulary, grammar, and pragmatics. While no amount of empirical inquiry can set out what counts as engaging, or too short, too long, too difficult, too easy or insufficiently responsive to the needs of a particular group of learners, a considerable body of SLA research has illuminated more broadly how materials m...