He's 3.
Each child is different.
My son, at 2 then 3 then now 4... "bonds" with me differently. Versus how my daughter was.
My son now at 4... is attached to me differently now... close to me and wanting me in a different way then when he was 3. Hard to describe... but developmental.
Or maybe, are there issues with the other kids? Some kids are sensitive to the "vibes" of other kids... and THEIR behavior or temperaments.... and some kids are just not nice.
Does your child LIKE the Teacher??? You said he likes the activities... but so, how does he like the Teacher???? Or her style of handling the kids????
Maybe, just be a fly on the wall one day... and observe the class and the Teacher and kids....
CONTINUE to allow him to express himself to you, though. Always....
all the best,
Susan