This chapter examines the emergence of big data in the field of education by showing how the idea of big data travels across levels and what happens when it does. The analysis in the chapter shows how the idea of big data is institutionalized within the field of education both globally and in the public education sector in Denmark. The OECD is a key actor in developing the idea of big data in education, while the Ministry of Education in Denmark absorbs the idea of big data in a pragmatic way by adopting governance-by-data. However, the two cases show that school leaders in Denmark manually try to ‘dig’ into or ‘meld’ the available data sets at a school level. The chapter concludes that there is a discrepancy between the high level of expectation of big data at transnational and national levels and how school leaders use data at school level. The closer the idea of big data gets to practice level, the more difficult it becomes to use data.