E.P.
My daughter by-passed the terrible two's but entered into the really challenging three's. They are really practicing their independence and it tests your patience. Could be a phase, if it is a phase, it will pass if you truly think he is doing this on purpose. Ignoring it is a good thing. He'll get bored by not getting a rise out of you. Don't be too concerned about not being focused in pre-school. They really are very young at this age and this is the first structured school situation that he has probably been in - he may be ready scholastically but possibly not socially. That will come in time.
Have you ever had him pre-school tested? School districts do it free of charge at certain times of the year. They do speech, cognitive, small & large motor skill testing and other age-appropriate developmental testing. It's worth getting tested - check with your local school district for preschool testing dates. I'm certain your area has some type of testing program.
Good Luck!