English teacher was from the UK. I'm Australian.
http://www.languagehat.com/archives/001730.php - some info i found.
"Traditionally, educated Australians have sanctioned only the "tray" pronunciation, regarding the alternative as clear evidence of illiteracy."
Looks like you learned something regardless, so when that old guy keeps saying trays you won't think he's retarded.
(I realize now that one is no more correct than the other btw).