I didn't read all the responses, but I wanted to say ditto to AmyB & Wenda. Especially about being appalled by the teacher's reaction. I definitely wouldn't give up on preschool (sounds like your son is just slow to warm up, but once he finds his routine he's grooving)...but the teacher's reaction makes me question how good/helpful/understanding/experienced/etc this particular school and teacher are.
Jumping into personal history:
My son went into 3day a week preschool *relatively* easily when he was 3 (he was soooo ready, and never wanted to leave when it was time to go kind of thing, but the new routine was definitely a little scary for him in the beginning). After the first couple weeks it was his favorite place in the world. (Ahem, still kind of is, we visit a couple times a year just so he can hug his teachers, and "chat").
- Same school a year later, and I had begun working a 12 hour shift on Mondays whereas previously I had only worked nights when my son was asleep. The teacher noticed my son was having consistently lousy Tuesdays (and we were in a montessori program that needs 3 days in a row, etc etc etc). So instead of suffering through, she brings up tuesdays, and offers to split his week to M, W, Th. So he could be home with me on tuesdays (and see if tuedays he was just missing Mom-time from the day before), but still stay with the same group of kids that he was friends with rather than move to the W/TH/Fri group.
- When he went through a "I'm not gonna get dressed in the morning without throwing a tempertantrum from blazes", which made us late a few times, she laughed and said to "bring him in his PJs, with his clothes in a bag...don't worry, with all the OTHER kids being dressed, he'll be changed lickedy split" (lol ... after the one time of wearing pjs to school, he only refused 2 more times to get dressed, but then got dressed in the car, rather than be odd man out).
- When any of the kids started saying mean things or going through a hitting phase her term was "so and so is learning to be a good friend, but is still working on X...there was some ______ing today and your son was really brave and patient etc" or vice versa if MY son was haveing trouble "learning to be a good friend", I'd get the low down on what went on and what steps were taken, AS WELL AS how "proud she was of him for x" (apologizing, listening, or some other activity he did well that day)...all right in front of him. So it was done in a way that encouraged good behavior from him, and helped ME out bigtime.
Tons and tons and tons of other examples leap to mind. In essence, I NEVER felt uncomfortable, there was always some positive spin, or aspect...and lots and lots of working together with his teacher. From day one I knew my son was safe and well cared for by this very experienced teacher and that her assistants were learning, too. I knew there'd be ups and downs, but that his teacher would help him through them...AND help me through them. Actually, since we now homeschool...I can officially say that she's my hero.