S.K.
It really depends on why he is daydreaming. A few reasons...
Is he advance, gets his work done and then is bored... daydreaming to entertain himself?
Does he crave an outlit for his creative side?
Is he stressed and day dreaming is an escape?
Is he 6 years old with a fantastic imagination? Who would want to focus on mundane school- repetative assignments that are supposed to fit every learning style, when they could be fully involved in a facinating day dream...
Is there too much stimulation in the classroom and he can't focus?
1st grade classes have very busy walls that tend to be very over stimulating.
Maybe he has a lot on his mind. Ask him.