Unchartered which uses Google books to look at how language has changed over time (or at least at the point where I am reading). But in the introduction Raj Chetty is referred to for his landmark study on the value added of a great teacher. Chetty earned the incredibly prestigious John Bates Clark award which often comes before a Noble Prize - and he is only 34! At any rate the paper concludes that when a high value added (VA) teacher joins a school, test scores rise immediately in the grade taught by that teacher; when a high VA teacher leaves, test scores fall. Test scores change only in the subject taught by that teacher, and the size of the change in scores matches what we predict based on the teacher’s VA .. and students assigned to such high value-added teachers are more likely to go to college, earn higher incomes, and less likely to be teenage mothers. On average, having such a teacher for one year raises a child's cumulative lifetime income by $80,000. Best of all the study is a quantitative one so it is not based on time based case studies so you can draw the inference that by reflecting and continuing to improving your craft you are really making a difference in the life of your students.