The study was conducted in 20 intact classes in grades 6 and 7 from suburban schools in Perth, Australia. The study investigated changes in discourse attributable to the use of an extended teacher wait time in a sequence of seven lessons related to probabilistic reasoning. A wait time feedback group of 10 classes obtained a significantly higher summative achievement mean than a control group that utilized a normal wait time. The results indicated that teacher wait time increased significantly over a seven lesson sequence from an average of 1.9 seconds to an average of 4.4 seconds. Discourse patterns in whole class settings also changed throughout the study. Although the total number of utterances decreased, the average length of pupil utterances increased. Changes were also observed in the teacher discourse. The most notable of these related to the type of teacher talk that followed a pupil response to a question. Teachers tended to probe to obtain further pupil input rather than mimicking pupil responses. The average length of student discourse and the proportion of student reacting were significantly related to summative achievement. The results of the study have indicated that the use of an extended teacher wait time in whole class settings can improve teacher and pupil discourse characteristics. However, the changes that occur are different to those that occur when an extended wait time is used in work groups. Teachers may need to be sensitized to the differing effects of longer wait time in whole class, work group, and individualized settings.