This paper describes the assessment understandings and practices of teachers at Central Park East Secondary School in the 1980s and 1990s, when the school was America's the leading effort to offer progressive education to poor urban youth. We found that teachers deployed technical assessment knowledge and had a strong sense of what they were assessing, how to assess it, how to score it, and how to weigh competing interpretations of the data. Still, they struggled with a number of dilemmas: in particular, how to address the competing claims of interdisciplinary, problem-based studies and disciplinary content knowledge. Our findings suggest the viability of teacher capacity building rather than accountability in school improvement.