Data has always been central to large-scale educational assessments, such as those provided by Cambridge Assessment, but digital learning and assessment products vastly increase the amount, types, and immediacy of data available. Advances in data science and technology have opened up this data for analysis as never before and "big data" is much hyped by both those that fear it and those that welcome it. But, as yet, there has been no big data revolution in education. In this article, I briefly outline current uses of data analytics at Cambridge Assessment, and how big data extends them. I explore some likely future uses and benefits of big data in relation to formative assessment and individualised recommendations for learners, together with the risks of statistical naivety and data misuse, and the challenge of gaining the trust of students, parents and teachers.