This position paper uses the concept of "hidden curriculum" as a heuristic device to analyze everyday data-related practices in formal education. Grounded in a careful reading of the theoretical literature, this paper argues that the everyday data-related practices of contemporary education can be approached as functional forms of data literacy education: deeds with unintentional educational consequences for students' relationships with data and datafication. More precisely, this paper suggests that everyday data-related practices represent data as cognitive authority and naturalize the routines of all-pervading data collection. These routines lead to what is here referred to as "data (il)literacy" -- an uncritical, one-dimensional understanding of data and datafication. Since functional data (il)literacy education takes place subconsciously, it can be conceptualized as a form of hidden curriculum, an idea that refers to lessons taught and learned but not consciously intended to be so.