In an attempt to get a general discussion going... This article, "The Injustice of Singer/Non-Singer labels by Music Educators" by Colleen Whidden is long, but interesting: http://www.queensu.ca/music/links/gems/Whidden5.pdf
It's about people who believe that they can't sing because someone told them they couldn't. There are some interesting observations in the article:
"A second reason for adult non-singers to label themselves as unmusical is that in a culture where nonmusical members are accepted and expected, some citizens feel the pressure and judgment of a society that does not allow a spectrum of musical ability. If one does not have a successful performance career in singing, then it is safer to never attempt a vocal sound."
"Finally, one of the most common reasons for adult non-singers to view themselves as unmusical is adult non-singers received negative feedback when they at some point in their life attempted to sing in a public setting. A significant number of research studies report that adult non-singers endured a negative childhood experience and this experience has played a crucial role in later life."
That's really sad. The article goes on to describe people who haven't been willing to sing so much as "Happy Birthday" for decades due to having been told by a grade school teacher that they can't sing.
In my own case, part of the reason I sing now is because an authority figure once took me aside and told me that I *could* sing.
Have others had experiences with a teacher who really encouraged or discouraged them in their singing or other musical efforts?