This paper provides an empirical account of the complex nature of early childhood teachers' work with growing accountability demands for collecting, reporting, and using child assessment data in the U.S. context. Particularly, this paper focuses on preschool teachers' experience of changes in their roles and pedagogical work in implementing a criterion-referenced, commercial online child assessment system. In doing so, this paper draws on data from a qualitative research study conducted at four Head Start sites that included semi-structured, individual interviews with six teachers and five child development specialists during three different assessment checkpoint periods; multiple observations of four Head Start classrooms for five months; and an analysis of related documents. The findings from this paper highlight that the use of commercial online childhood assessment system increased and expanded teacher work with additional responsibilities and concomitant change in assessment, curriculum, and pedagogy, as well as their views of themselves as professionals.