At my old eikaiwa job, everyone said "o-tsukare-sama deshita" to me when I finished work. At my high school, all of the teachers say "sayonara". Previously, I never heard "sayonara" used in this situation, and I was told that "sayonara" usually (informally) implies a final farewell.
Does anyone know if this choice of words is due to a difference in working culture between private businesses and public high schools?
I also thought it might be because they underestimate my Japanese ability, and think that I wouldn't understand "o-tsukare-sama". But I had to give a 3-4 minute speech in Japanese on my first day of work, so they know that I've worked in a Japanese environment before and I can speak the language, at least enough to fire off a simple "o-tsukare-sama deshita" at the end of the day.
I leave at 3:15 and the regular teachers leave at 5:00, so I'm never around to hear what they say to each other at the end of the day.