At the simplest level, teacher talk time (TTT) refers to how much the teacher talks during a lesson. However, this will vary according to the stage of the lesson. For example, the teacher needs to speak more when providing explanations of and examples for the target language early in the lesson. These moments have activities and practices more teacher-centered. The adequate teacher talking time is 30% for these moments. Elsewhere he may speak less as students need ample opportunity to practice the new material. This is when learner-centered activities take place and adequate TTT is 20%.
Overall, however, the teacher should roughly limit his speaking to 20% to 30% of the class time, with the remainder devoted to speaking/use of the language by the students.
On the other hand, Student Talk Time (STT) should be around 80% during the course of the lesson.
Hey teachers, beware your TTT!!! :)