I would think the pre school Teacher would be observing all the time sounds like she is putting the issue back on you, hes only 3 years old,maybe they should be observing more, I wonder how many kids top each Teacher there are, it doesnt sound like he needs evaluating yet if he shows a lot more distraction you perhaps would put your own mind at rest to ask a councillor.or chanmge your school.
3 years old is too young to be evaluated for anything unless he is very behind in his development and/or showing very strong emotional/ aggressive tendencies. Most 3 year olds can't pay attention for very long.
It sounds like a very structured preschool. Perhaps something less structured would work for him.
THANKS FOR YOUR COMMENTS!