Quotations on teacher and teaching

Think Exist is a repository of quotations, including quotes on teachers and teaching, ranging from the sad (but often heard throughout these last 25 years)

"He who can, does. He who cannot, teaches.”
(by George Bernard Shaw) 

to the inspiring 

"The mediocre teacher tells. The good teacher explains. The superior teacher demonstrates. The great teacher inspires.” 

(by William Arthur Ward).