Recent interest in the direct, descriptive study of teaching has led to renewed attention to the types of questions asked by teachers. An important contributing factor has also been the progress made in the analysis of cognitive operations and the identification of a complex hierarchy of operations. Several observation systems developed from Bloom's taxonomy have been used by the authors to study the cognitive levels of teachers' questions. These studies pointed the direction toward research presently underway and planned. They also made possible the development of the Questioning Strategies Observation System, which records not only the cognitive levels of teachers' questions, but also other behaviors related to successful questioning strategies. The system has been designed so that it may be used both with live observation and with tape recordings of teachers' classroom verbal behavior. (RT)