This week is "Teacher Appreciation Week". I didn't know it until I saw the Huffington Post article "Teacher Appreciation Quotes: Famous Sayings For Teachers And About Teaching".
My favorites was
"In teaching you cannot see the fruit of a day's work. It is invisible and remains so, maybe for twenty years." - Jacques Barzun
If this isn't a rebuke of merit pay and the idea of easily measurable teacher performance, I don't know what is.
However, one of the commenters (LeoWong) to the article wrote that Barzun didn't write this, but about the artistic or intellectual life.
I looked and looked for a more direct attribution but could only find the same quote over and over again with no source citation other than Jacques Barzun.
So, I wrote a WikiQuote entry to ferret out some more information. We shall see what happens. [It was deleted. I won't go into the reasons here.]