With so much emphasis on teacher quality it is worth considering the power of non verbal communication in pedagogy.
Teachers who smile, laugh and move around the room are more successful at achieving good student outcomes. Non verbal communication is often more powerful than the spoken word.
Research (Ambady & Rosenthal, 1993) found that students were able to accurately judge good teachers from small video clips (less than 30 seconds) of their teaching style. The students picked the teachers who also had the best end of semester results and even more surprising, the student choices were identical to the choices made by principals, who were also asked to choose good teachers from the short clips.
Threatening, cranky and stressed teachers have difficulty positively engaging students in learning.