Teacher quality more heavily influenced differences in student performance than did race, class or school of the student; disadvantaged students benefited more from good teachers than advantaged students.
— Nye, Konstantopoulos & Hedges, 2004

The quality of teacher-student relationships is the keystone for all other aspects of classroom management.  In fact our meta-analysis indicates that on average, teachers who had high quality relationships with their students had 31% fewer discipline problems, rule violations, and related problems over a year’s time than did teachers who did not.
— Robert  Marzano

Eric Hanushek, an education economist at Stanford University estimates that the students of a very bad teacher will learn, on average, a half year’s worth of material in one school year.  The students in the class of a very good teacher will learn a year and a half’s worth of material. Teacher effects dwarf school effects:  your child is actually better off in a “bad” school with an excellent teacher than in an excellent school with bad teacher.

Students assigned to a good teacher for three years in a row will score 50 percentile points higher on tests than students assigned to a weak teacher over the same period.
— William Sanders

Teacher quality matters.  In fact, it is the most important school-related factor influencing student achievement.
— Jennifer King Rice

Achievement gains from having an effective teacher could be almost three times as large for African American students than for white students, even when comparing students with their prior school achievement.
— Sanders & Rivers, 1996

…feedback, a direct personal response by a teacher to a specific statement by a student—seems to be the most closely linked to academic success.
— Bob Pianta, dean of the University of Virginia’s Curry School of Education