When testing dominates decisions about instruction in public schools, complex interactions significant to how students actually learn are often ignored. Teachers who critically interrogate conflicts between institutional policies and practices, such as testing and instruction, position themselves as informed, active, and professionally responsible to students. Here, the work of a collaborative inquiry group of four novice urban elementary teachers and a university partner supports such a stance. Through critical reflection on test practices, these teachers developed "knowledge of practice," and made productive use of uncertainty and diversity to encourage inclusive instruction in their local contexts. (Contains 1 footnote.)