From NPR via Education Dive:

“Research has found a direct correlation between student success and teacher stress; social adjustment and academic performance of students suffers when the teacher are not happy… Research also suggests that promoting mindfulness training for teachers is helpful for improving their sentiments about the job.”

http://www.educationdive.com/news/study-finds-teacher-stress-levels-on-par-with-those-of-physicians-and-nurse/433132/