I'm a SAHM and my kids didn't go to daycare. I ran a home daycare while they were little to allow them to stay with Mom and allow me to earn money. Here in Georgia we have the government sponsored 4-K. Both my kids had their first school/daycare experience at age 4. They were quite able to speak and tell me all about their day.
One day my youngest came home and was very upset because he got sent to the director's office- quite unusual for him as he was a very well behaved child. He cried and told me they yelled at him and he had to sit in the office for all day.
The next day when I dropped him off at school, I asked to speak to the teacher about his behavior. She laughed and assured me that it wasn't major and she was just trying to instill in him the fact that he HAD to follow the teacher's rules. He wasn't being bad but just having selective hearing when it was time to line up for bathroom break. She had taught 4-k for 25 years and I was very comfortible with her as a teacher. She said in her experience that the "good" kids just have to try the limits once in a while and she tried to stop them before they are hard to real in. She did raise her voice and sent him to the director. The director only said to him that he had to sit with her for a while- they gave him a 5 min. time-out. It was very scarry to him as he thought he was in major trouble-
I've never had any behavior trouble out of him in school again, he's in second grade this year. The experience left a lasting impression.
While a just turned three may not able to fully explain what happened, he did let you know he was upset- I would persue the issue and tell them to call you next time there is a question about his behavior, that you do not condone raised voices in the classroom, that he is a very sensitive child and suggest other ways to curb any questionable behavior that may occure.
They probably just sent him to the office to scare him into behaving- sometimes the teacher needs a time-out from a busy child and it may be better for him to leave the room if he is getting on her nerves. Better yet- are there any other rooms for three year olds there that he may switch too?