Self-Fulfilling Expectations

"As long as [something] isn't total crap, your experience will match up with your expectations."
http://lifehacker.com/5990737/why-we-cant-tell-good-wine-from-bad

In education, the urban legend always was that if students' locker numbers were randomly substituted for their IQ scores, and when these artificial values were passed on to their teachers, then students' subsequent learning assessments by their teachers would tend to correlate with the values of the locker numbers. 

This story most often makes we educators cranky.

Probably not true at the extremes, but in the 'great muddy middle', one ought to carefully consider the influences of our expectations on outcomes.