Elementary science teachers allow an average of one second for a response to a question, and follow a student response by a comment within an average of nine-tenths of a second. When these two "wait times" are extended to three to five seconds, a number of changes occur in student variables. There are increases in the length of the response, the number of unsolicited appropriate responses, student confidence, incidence of speculative responses, incidence of child-child data comparisons, incidence of evidence-inference statements, frequency of student questions, and incidence of responses from "relatively slow" students. The number of teacher questions which do not elicit a response decreases. Teacher characteristics change as wait-times increase. There is an increased flexibility of teacher responses, the questioning pattern becomes more variable, teacher expectations for performance of students rated as "slow" may change. These generalizations are based upon five years of study of video-taped lessons or micro-teaching sessions. These studies also suggest some research hypotheses concerning the effect of verbal reward and wait-time on students' perceptions of their degree of environmental control: low incidence of verbal reward and a long wait-time may reduce fatalism. (Author/AL)