This paper explores how data-driven practices and logics have come to reshape the possibilities by which the teaching profession, and teaching professionals, can be known and valued. Informed by the literature and theorising around educational performativity, the constitutive power of numbers, and affective responses to data, it shows how different US educators experienced, and came to embody, new forms of numbers-based accountability. Drawing on interviews with teachers, and school- and district-level leaders, as well as relevant school-based documents, it is argued that such data are now both "effective" (i.e. they change 'what counts' within the profession) and "affective" (i.e. they produce new expectations for teachers to profess data-responsive dispositions over actual educative practices). This prevalence and use of data have combined not only to change teaching into a 'data profession', but also to change teachers into 'professors' of data.