An online learning system in support of active learning and formative evaluation via a teaching-by-questioning strategy in classrooms was developed. Following a design-based research paradigm, the theoretical base, design principles, and associated spaces for the system were explicated. Its learning potential in terms of perceived usefulness, ease of use, and relative advantage was evaluated in an undergraduate engineering class by mixed methods research. Quantitative data from an end-of-semester questionnaire supported the learning usefulness of teaching-by-questioning on the developed system for the promotion of various cognitive and higher-order thinking processes regarded as important in active classrooms as well as its ease of use. Moreover, the results of the chi-square test indicated that substantially more participants supported the developed system over Facebook for promoting learning, and explanatory data further highlighted the developed system's distinct feature of deferring display of participants' responses to stimulate independent thinking and support meaningful formative evaluation.